Implement encoder interface (still preliminary)

 - Implement OBS encoder interface.  It was previously incomplete, but
   now is reaching some level of completion, though probably should
   still be considered preliminary.

   I had originally implemented it so that encoders only have a 'reset'
   function to reset their parameters, but I felt that having both a
   'start' and 'stop' function would be useful.

   Encoders are now assigned to a specific video/audio media output each
   rather than implicitely assigned to the main obs video/audio
   contexts.  This allows separate encoder contexts that aren't
   necessarily assigned to the main video/audio context (which is useful
   for things such as recording specific sources).  Will probably have
   to do this for regular obs outputs as well.

   When creating an encoder, you must now explicitely state whether that
   encoder is an audio or video encoder.

   Audio and video can optionally be automatically converted depending
   on what the encoder specifies.

   When something 'attaches' to an encoder, the first attachment starts
   the encoder, and the encoder automatically attaches to the media
   output context associated with it.  Subsequent attachments won't have
   the same effect, they will just start receiving the same encoder data
   when the next keyframe plays (along with SEI if any).  When detaching
   from the encoder, the last detachment will fully stop the encoder and
   detach the encoder from the media output context associated with the
   encoder.

   SEI must actually be exported separately; because new encoder
   attachments may not always be at the beginning of the stream, the
   first keyframe they get must have that SEI data in it.  If the
   encoder has SEI data, it needs only add one small function to simply
   query that SEI data, and then that data will be handled automatically
   by libobs for all subsequent encoder attachments.

 - Implement x264 encoder plugin, move x264 files to separate plugin to
   separate necessary dependencies.

 - Change video/audio frame output structures to not use const
   qualifiers to prevent issues with non-const function usage elsewhere.
   This was an issue when writing the x264 encoder, as the x264 encoder
   expects non-const frame data.

   Change stagesurf_map to return a non-const data type to prevent this
   as well.

 - Change full range parameter of video scaler to be an enum rather than
   boolean
Add atomic increment/decrement platform funcs
Call send_packet instead of..  doing nothing

GCC warned of this, but strangely not clang.
Add Qt5 to includes (caused issues with debian) *

* Not entirely sure if this will fix it, johnnypatterson claimed it
  would, but this checked out on my mac so at the very least I don't
  think it should hurt anything
Set defaults automatically

Automatically query defaults for sources/outputs/encoders and set them
before calling create
Use atomic functions where appropriate

Also, rename atomic functions to be consistent with the rest of the
platform/threading functions, and move atomic functions to threading*
files rather than platform* files
Fix Qt5 with debian-based builds (for real)

You have to use qt5_use_modules otherwise it just won't always work.  I
don't know how it was working before with cmake, but apparently this
does the trick to ensure that all the necessary libraries and includes
are added.  ..Might require cmake 3.8.9 though.  ..I do hope that
doesn't end up being a problem.
Change a reference variable to be volatile long

Removed some warnings associated with it, was the wrong variable type.
obs-data: Internally store as int or double

If integers are used, then store as integers.  If doubles are used, then
store as doubles.  This way precision issues are prevented.
Make sure ot use the right enum name

Microsoft's garbage compiler just doesn't even..  read the names of
enums.  It sees an enum and goes "durr, that's an int" without even
properly evaluating it.  Just total garbage, as per usual.