Adds functions to turn on audio monitoring to allow the user to hear
playback of an audio source over the user's speaker.  It can be set to
turn off monitoring and only output to stream, or it can be set to
output only to monitoring, or it can be set to both.

On windows, audio monitoring uses WASAPI.  Windows also is capable of
syncing the audio to the video according to when the video frame itself
was played.

On mac, it uses AudioQueue.

On linux, it's not currently implemented and won't do anything (to be
implemented).

From 0.0 (not congested) to 1.0 (completely congested/dropping).

Uses the libcaption library to allow insertion of caption data directly
in to H.264 frame data.

Prevents reallocation of encoded packet data.

Deprecates:
obs_duplicate_encoder_packet
obs_free_encoder_packet

Replaces those functions with:
obs_encoder_packet_ref
obs_encoder_packet_release

There's no need to have two separate macros to declare something as
deprecated.

Allows getting the current active framerate that the core is rendering
with.  This takes in to account any rendering lag or stalls that may be
occurring.

Allows the ability to use scale filters such as point, bicubic, lanczos
on specific scene items, disabled by default.  When using one of the
latter two options, if the item's scale is under half of the source's
original size, it uses the bilinear low resolution downscale shader
instead.

(Note: this commit also modifies the obs-filters and test-input modules)

Changes the obs_source_process_filter_begin return type so that it
returns true/false to indicate that filter processing should or should
not continue (for example if the filter is bypassed or if there's some
other sort of issue that causes the filtering to fail)

Allows the ability to mark an encoder as deprecated (such as the media
foundation h264 encoders)

This is a band-aid solution to be able to create temporary services
without logging them and keep them out of enumeration functions.

This is a band-aid solution -- 'master obs context lists' should not be
kept by the core.  Logging of object creation/destruction should also be
controlled by the front-end instead of the core.

Determines whether an obs object was created successfully.  If a plugin
that's used for a saved object is removed (third party plugins), its
data will become invalid, but the objects can often still be created for
the sake of preserving user settings, but sometimes these objects can
cause problems if they're actually used (such as using them for
transitions).

Renders the scene item to a texture if crop is enabled; otherwise
renders directly.

Allows the ability to defer updating the item transform until all
functions have been executed.

Adds deinterlacing API functions.  Both standard and 2x variants are
supported.  Deinterlacing is set via obs_source_set_deinterlace_mode and
obs_source_set_deinterlace_field_order.

This was implemented in to the core itself because deinterlacing should
happen before effect filters are processed, but after async filters are
processed.  If this were added as a filter, there is the possibility
that a different filter is processed before deinterlacing, which could
mess with the result.  It was also a bit easier to implement this way
due to the fact that that deinterlacing may need to have access to the
previous async frame.

Effects were split in to separate files to reduce load time (especially
for yadif shaders which take a significant amount of time to compile).

Kindly ignore this commit, this is to prove that this is also my email.

(Note: This commit also changes the UI)

Changed:
-------------------
void obs_load_sources(obs_data_array_t *sources_list);

To:
-------------------
void obs_load_sources(obs_data_array_t *sources_list,
		obs_source_load_cb callback, void *private_data);

Signals should really never be required to use to make some function
work properly.  The "source_load" signal was required for the
obs_load_sources function, but it's meant more for loading private data
in the settings, not for general loading of sources.

This changes it so that a callback is explicitly required to load the
sources.

(Note: This commit also modifies the UI)

Allows the ability to duplicate sources fully copied, and/or have the
scene and its duplicates be private sources

Creates a scene marked as a private source

Allows full duplication of sources (with exception of sources that are
marked with the OBS_SOURCE_DO_NOT_DUPLICATE output capability flag)

Mostly only used for transitions with the intention of automatically
creating transitions which don't require configuration, returns whether
the source has any properties or not (whether it's configurable)

Allows creation of private/unlisted sources/outputs/services/encoders

(Note: This commit also modifies UI)

Instead of using signals, use designated callback lists for audio
capture and audio control helpers.  Signals aren't suitable here due to
the fact that signals aren't meant for things that happen every frame or
things that happen every time audio/video is received.  Also prevents
audio from being allocated every time these functions are called due to
the calldata structure.

Transition sources are implemented by registering a source type as
OBS_SOURCE_TYPE_TRANSITION.  They're automatically marked as video
composite sources, and video_render/audio_render callbacks must be set
when registering the source.  get_width and get_height callbacks are
unused for these types of sources, as transitions automatically handle
width/height behind the scenes with the transition settings.

In the video_render callback, the helper function
obs_transition_video_render is used to assist in automatically
processing and rendering the audio.  A render callback is passed to the
function, which in turn passes to/from textures that are automatically
rendered in the back-end.

Similarly, in the audio_render callback, the helper function
obs_transition_audio_render is used to assist in automatically
processing and rendering the audio.  Two mix callbacks are used to
handle how the source/destination sources are mixed together.  To ensure
the best possible quality, audio processing is per-sample.

Transitions can be set to automatically resize, or they can be set to
have a fixed size.  Sources within transitions can be made to scale to
the transition size (with or without aspect ratio), or to not scale
unless they're bigger than the transition.  They can have a specific
alignment within the transition, or they just default to top-left.
These features are implemented for the purpose of extending transitions
to also act as "switch" sources later, where you can switch to/from two
different sources using the transition animation.

Planned (but not yet implemented and lower priority) features:

- "Switch" transitions which allow the ability to switch back and forth
  between two sources with a transitioning animation without discarding
  the references

- Easing options to allow the option to transition with a bezier or
  custom curve

- Manual transitioning to allow the front-end/user to manually control
  the transition offset

(Note: test and UI are also modified by this commit)

API Changed (removed "enum obs_source_type type" parameter):
-------------------------
obs_source_get_display_name
obs_source_create
obs_get_source_output_flags
obs_get_source_defaults
obs_get_source_properties

Removes the "type" parameter from these functions.  The "type" parameter
really doesn't serve much of a purpose being a parameter in any of these
cases, the type is just to indicate what it's used for.

The new audio subsystem fixes two issues:

- First Primary issue it fixes is the ability for parent sources to
  intercept the audio of child sources, and do custom processing on
  them.  The main reason for this was the ability to do custom
  cross-fading in transitions, but it's also useful for things such as
  side-chain effects, applying audio effects to entire scenes, applying
  scene-specific audio filters on sub-sources, and other such
  possibilities.

- The secondary issue that needed fixing was audio buffering.
  Previously, audio buffering was always a fixed buffer size, so it
  would always have exactly a certain number of milliseconds of audio
  buffering (and thus output delay).  Instead, it now dynamically
  increases audio buffering only as necessary, minimizing output delay,
  and removing the need for users to have to worry about an audio
  buffering setting.

The new design makes it so that audio from the leaves of the scene graph
flow to the root nodes, and can be intercepted by parent sources.  Each
audio source handles its own buffering, and each audio tick a specific
number of audio frames are popped from the front of the circular buffer
on each audio source.  Composite sources (such as scenes) can access the
audio for child sources and do custom processing or mixing on that
audio.  Composite sources use the audio_render callback of sources to do
synchronous or deferred audio processing per audio tick.  Things like
scenes now mix audio from their sub-sources.

(Note: This commit breaks libobs compilation.  Skip if bisecting)

These variables are considered obsolete and will no longer be needed.

(Note: This commit breaks libobs compilation.  Skip if bisecting)

Removes audio lines and stores the circular buffer for the audio on the
source itself.

Allows getting the timestamp for the video frame currently being
rendered.

There shouldn't be any need to call these functions manually.  These
functions are called automatically by obs_save_sources and
obs_load_sources.

Before if a source was set to invisible it would still be considered
active.  This changes it so that the source is deactivated when the
source is invisible to reduce needless resource usage or capturing.

Renames:
----------------------------------------
obs_source_add_child
obs_source_remove_child
obs_source_enum_sources
obs_source_enum_tree
obs_source_info::enum_sources

To:
----------------------------------------
obs_source_add_active_child
obs_source_remove_active_child
obs_source_enum_active_sources
obs_source_enum_active_tree
obs_source_info::enum_active_sources

These functions/callbacks had misleading names: they originally implied
any child sources, when they actually meant active child sources that
are being used to render video or audio.  It's important that the
function names represent their actual purpose.

(Note: This commit breaks UI compilation.  Skip if bisecting)

Adds a means of saving specific sources that the front-end chooses,
rather than being forced to use the now-removed "user list".

(Note: This commit breaks UI compilation.  Skip if bisecting)

API Removed:
------------------------
obs_add_source

API Changed:
------------------------
obs_source_remove: Now just marks/signals a source for removal

The concept of "user sources" is flawed: it was something that the
front-end was forced to deal with if it wanted to automate source
saving/loading, and often it had to code around it.  That's not how
saving/loading should work, a front-end should be allowed to manage
lists of sources in the way it explicitly chooses, and it should be able
to choose which sources it wants to save/load.

This function was removed even though the browser plugin was using this
function on mac, so this is being put back in temporarily while the
browser plugin is modified to remove this function.