Also make the ReadCloser an Controllable allows to uncouple
the controller implementation from the encoder.
This is not needed for the 2 codec controller already implemented (openh264 and vpx)
but is more future proof in case it required for other codecs.
With webrtc v3, users no longer need to bind or unbind manually anymore.
Changes:
* Switch from webrtc.RTPCodec to webrtc.RTPCodecParameters
* Fix broken examples after the upgrade
* NewRTPReader now accepts ssrc as a parameter
* Track interface now fulfills webrtc.TrackLocal requirements
Resolves https://github.com/pion/mediadevices/issues/114
* Remove codec registrar
* Completely redesign how codec is being discovered, tuned, and built
* Update examples
* Update unit tests