Fixes #1742
Fixes #2021

* get_source_code_async
* fetch_module_meta_data_async
* fetch_module_meta_data_and_maybe_compile_async

They do not depend on DenoDir, so should not be methods of it.

To better distinguish the deno_core crate from the executable deno,
which will now be called "the cli" internally.

Operating systems have defined directories for cache files.
That allows them to do smart things such as leaving them out when doing a backup,
or deleting them when disk space gets low.

Also a %home%\.deno folder on windows made no sense whatsoever.

Fixes #481

Fixes #472

Move module stuff into its own file.

Allows for future asynchronous module loading.

Add support for import.meta.url

Fixes #1496

It should return an error if a file with the given path exists and
recursive isn't specified.

Because mode is not used on windows and rarely used in unix, it is made
to the last parameter.

In collaboration with Stefan Dombrowski <sdo451@gmail.com>

* Native ES modules

This is a major refactor of internal compiler.

Before: JS and TS both were sent through the typescript compiler where
their imports were parsed and handled. Both compiled to AMD JS and
finally sent to V8

Now: JS is sent directly into V8. TS is sent through the typescript
compiler, but tsc generates ES modules now instead of AMD. This
generated JS is then dumped into V8.

This should much faster for pure JS code. It may improve TS compilation
speed.

In the future this allows us to separate TS out of the runtime heap and
into its own dedicated snapshot. This will result in a smaller runtime
heap, and thus should be faster.

Some tests were unfortunately disabled to ease landing this patch:
1. compiler_tests.ts which I intend to bring back in later commits.
2. Some text_encoding_test.ts tests which made the file invalid utf8.
   See PR for a discussion.
Also worth noting that this is necessary to support WASM

This reverts commit e976b3e0.

There is nothing technically wrong with this commit, but it's adding
complexity to a big refactor (native ES modules #975). Since it's not
necessary and simply a philosophical preference, I will revert for now
and try to bring it back later.

This bring it inline with terminology used in V8
See ResolveCallback in v8.h

- Improves speed and binary size significantly.
- Makes deno_last_exception() output a JSON structure.
- Isolate::execute and Isolate::event_loop now return
  structured, mapped JSError objects on errors.
- Removes libdeno functions:
  libdeno.setGlobalErrorHandler()
  libdeno.setPromiseRejectHandler()
  libdeno.setPromiseErrorExaminer()

In collaboration with Ryan Dahl.