Add the ability to be able to call and use toolkit-specific or
program-specific user interface in modules.

User interface code can be either bundled with the module, or 'split'
out in to separate libraries (recommended).

There are three reasons why splitting is recommended:

  1.) It allows plugins to be able to create custom user interface for
      each toolkit if desired.

  2.) Often, UI will be programmed in one language (the language of the
      toolkit), and core logic may be programmed in another.  This
      allows plugins to keep the languages separated if necessary.

  3.) It prevents direct linkage of UI toolkits libraries with core
      module logic.

Splitting is not required, though is recommended if you want your plugin
to be more flexible with other user interface toolkits or programs.

Will implement a generic properties lookup next, which will be used for
automatic UI handling so that plugin UI isn't necessarily required.

- Add 'set_default' functions to obs-data.*.  These functions ensure
  that a paramter exists and that the parameter is of a specific type.
  If not, it will create or overwrite the value with the default setting
  instead.

  These functions are meant to be explicitly called before using any of
  the 'get' functions.  The reason why it was designed this way is to
  encourage defaults to be set in a single place/function.

  For example, ideal usage is to create one function for your data,
  "set_my_defaults(obs_data_t data)", set all the default values within
  that function, and then call that function on create/update, that way
  all defaults are centralized to a single place.

- Ensure that data passed to sources/encoders/outputs/etc is always
  valid, and not a null value.

- While I'm remembering, fix a few defaults of the main program config
  file data.

Add a fairly easy to use settings interface that can be passed to
plugins, and replaced the old character string system that was being
used before.  The new data interface allows for an easier method of
getting/altering settings for plugins, and is built to be serializable
to/from JSON.

Also, removed another wxFormBuilder file that was no longer in use.

Just a minor fix mostly because I noticed that I kept accidentally
forgetting to add checks to the code properly.  This is one of those
cases where macros come in useful, as macros can automate the process
and help prevent these mistakes from happening by accident.

- First, I redid the output interface for libobs.  I feel like it's
  going in a pretty good direction in terms of design.

  Right now, the design is so that outputs and encoders are separate.
  One or more outputs can connect to a specific encoder to receive its
  data, or the output can connect directly to raw data from libobs
  output itself, if the output doesn't want to use a designated encoder.
  Data is received via callbacks set when you connect to the encoder or
  raw output.  Multiple outputs can receive the data from a single
  encoder context if need be (such as for streaming to multiple channels
  at once, and/or recording with the same data).

  When an encoder is first connected to, it will connect to raw output,
  and start encoding.  Additional connections will receive that same
  data being encoded as well after that.  When the last encoder has
  disconnected, it will stop encoding.  If for some reason the encoder
  needs to stop, it will use the callback with NULL to signal that
  encoding has stopped.  Some of these things may be subject to change
  in the future, though it feels pretty good with this design so far.
  Will have to see how well it works out in practice versus theory.

- Second, Started adding preliminary RTMP/x264 output plugin code.

  To speed things up, I might just make a direct raw->FFmpeg output to
  create a quick output plugin that we can start using for testing all
  the subsystems.

Completely revamped the entire media i/o data and handlers.  The
original idea was to have a system that would have connecting media
inputs and outputs, but at a certain point I realized that this was an
unnecessary complexity for what we wanted to do.  (Also, it reminded me
of directshow filters, and I HATE directshow with a passion, and
wouldn't wish it upon my greatest enemy)

Now, audio/video outputs are connected to directly, with better callback
handlers, and will eventually have the ability to automatically handle
conversions such as 4:4:4 to 4:2:0 when connecting to an input that uses
them.  Doing this will allow the video/audio i/o handlers to also
prevent duplicate conversion, as well as make it easier/simple to use.

My true goal for this is to make output and encoder plugins as simple to
create as possible.  I want to be able to be able to create an output
plugin with almost no real hassle of having to worry about image
conversions, media inputs/outputs, etc.  A plugin developer shouldn't
have to handle that sort of stuff when he/she doesn't really need to.

Plugins will be able to simply create a callback via obs_video() and/or
obs_audio(), and they will automatically receive the audio/video data in
the formats requested via a simple callback, without needing to do
almost anything else at all.

- Add preliminary (yet to be tested) handling of timestamp invalidation
  issues that can happen with specific devices, where timestamps can
  reset or go backward/forward in time with no rhyme or reason.  Spent
  the entire day just trying to figure out the best way to handle this.

  If both audio and video are present, it will increment a reference
  counter if video timestamps invalidate, and decrement the reference
  counter when the audio timestamps invalidate.  When the reference
  counter is not 0, it will not send audio as the audio will have
  invalid timing.  What this does is it ensures audio data will never go
  out of bounds in relation to the video, and waits for both audio and
  video timestamps to "jump" together before resuming audio.

- Moved async video frame timing adjustment code into
  obs_source_getframe instead so it's automatically handled whenever
  called.

- Removed the 'audio wait buffer' as it was an unnecessary complexity
  that could have had problems in the future.  Instead, audio will not
  be added until video starts for sources that have both async
  audio/video.  Audio could have buffered for too long of a time anyway,
  who knows what devices are going to do.

- Fixed a minor conversion warning in audio-io.c

 - Often, timestamps will go "back" in time with certain..  terrible
   devices that no one should use.  When this occurs, timing is now
   reset so that the new audio comes in directly after the old audio
   seamlessly.

 - Added a volume variable to the obs_source structure and implemented
   functions for manipulating source volume.

 - Added a volume variable to the audio_data structure so that the
   volume will be applied when mixing.

  Scenes will now signal via their source when an item has been added
or removed from them.

  "add" - Item added to the scene.
  Parameters:  "scene": Scene that the item was added to.
               "item":  Item that was added.

  "remove" - Item removed from the scene.
  Parameters:  "scene": Scene that the item was removed from.
               "item":  Item that was removed.

add obs_source functions to allow name manipulation and lookup based upon name, and a few other functions related to getting/setting source information

add support for texture_rect texture type in shaders, add new form, clear up a few things in the API

With the permission of my fellow contributors, I'm switching obs-studio back to GPL v2+ to prevent issues between this project and the original OBS project, and for personal reasons to avoid legal ambiguity (not political reasons, I admittedly would prefer GPL v3+)

cleaned up main internal data structure design, changed to reference counting for sources to ensure safe destruction of source objects from all parts of the system, added some service-related stuff for testing

added support for jansson, added new output files, made some adjustments to the API, fixed a UI subclass issue

finish up most of the source audio stuff and rename some variables/structs/enum to be a bit more consistent

fill out the rest of the source video frame functions, added nv12 decompression function, and cleaned up the design of the source video frame stuff

added intial async audio/video code, fixed a few bugs, improved thread safety, and made a few other minor adjustments

change names, fix some bugs, minor GL/D3D fixes, update tests, fix effect files, output a little more debug information