Closes obsproject/obs-studio#1263

Adds obs_add_raw_video_callback() and obs_remove_raw_video_callback()
functions which allow the ability to get raw video frames without
necessarily needing to create an output.

Allows the ability to get the last rendered texture of the main output
view.

Closes jp9000/obs-studio#1203

Prevents SWIG from being able to process certain declarations that would
cause binding generation errors/warnings.

Allows the ability to have a callback invoked every time video ticks.
Particularly useful for scripting.

(Note: This commit also modifies UI and test)

This makes it so that main preview panes are rendered with the main
output texture rather than re-rendering the main view.  The view will
render all objects again, whereas the output texture will be a single
texture render of the same exact thing.

Also fixes some abnormal artifacting when scaling the main preview pane.

Decoupling the audio from the video causes the audio to be played right
when it's received rather than attempt to sync up to the video frames.
This is useful with certain async sources/devices when the audio/video
timestamps are not reliable.

Naturally because it plays audio right when it's received, this should
only be used when the async source is operating in unbuffered mode,
otherwise the video frame timing will be out of sync by the amount of
buffering the video currently has.

Allows setting and sharing of user data for sources and scene items.

Some plugins are using the OBS_VERSION macro obs-config.h to specify the
current version, which will bake the string in to the plugin, making it
so that if the plugin is not replaced for a patch, it could potentially
have the incorrect version.  This makes it so that a plugin/frontend can
get the current version string that's baked in to libobs itself.

This allows the ability for certain types of modules (particularly
scripting-related modules) to initialize extra data when all other
modules have loaded.  Because front-ends may wish to have custom
handling for loading modules, the front-end must manually call
obs_post_load_modules after it has completed loading all plug-in
modules.

Closes jp9000/obs-studio#965

For specific types of transitions (stingers in this case), there is no
blending done of the two targets, so wasting GPU resources rendering
them to textures is unnecessary.

Allows the ability to change the output type in case one service
requires a different output type.

NOTE: This should be considered a temporarily yet simple solution to a
specific problem: support for RTMP-like outputs.  This will allows
seamless integration of supporting different RTMP-like output types
within the same service.  This should probably be replaced with a more
ideal solution later, such as implementing a completely different
service type instead, when time permits.

(This commit also modifies obs-outputs)

Adds a lock checkbox to allow the user to lock a specific scene item.

Closes jp9000/obs-studio#949

Allows directly rendering a non-async source without going through
filters.

Adds a method of uniquely identifying scene items, as well as finding
those scene items via that unique ID.

(This commit also modifies the decklink, linux-v4l2, mac-avcapture,
obs-ffmpeg, and win-dshow modules)

Originally, async buffering for sources was supposed to be a
user-controllable flag.  However, that turned out to be less than ideal
because sources (such as the win-dshow plugin) were programmed with
automatic control over their buffering (such as automatically detecting
USB 2.0 capture devices and then enabling in those cases).

The fact that it was a flag caused a design flaw to where buffering
values would be overwritten when a source is loaded from save data.

Because of that, this flag is being deprecated and replaced with a
specific function to enable unbuffered mode instead.

Returns whether the output is currently in a state of reconnecting or
not.

Useful for rendering statistics.

Useful for real-time rendering statistics

Optionally allows drawing directly to the primary output instead of
having to use a source to draw.

Prevents any delay when starting up certain async video sources.
Additionally prevents old frames from being presented as well.

Closes jp9000/obs-studio#840

Allows copying filters from one source to another.

Closes jp9000/obs-studio#860

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.