Remove RTC prefix from all names

Let's pull off the bandaid!

* Reduces studdering: webrtc.RTCTrack -> webrtc.Track
* Makes it easier to find types by editor autocomplete
* Makes code read more fluently (less repetition)

Since we're breaking the API in 2.0, our only chance to
do this is now.

Relates to #408

rtcrtpcodingparameters.go

@@ -1,9 +1,9 @@
 package webrtc
 
-// RTCRtpCodingParameters provides information relating to both encoding and decoding.
+// RTPCodingParameters provides information relating to both encoding and decoding.
 // This is a subset of the RFC since Pion WebRTC doesn't implement encoding/decoding itself
 // http://draft.ortc.org/#dom-rtcrtpcodingparameters
-type RTCRtpCodingParameters struct {
+type RTPCodingParameters struct {
 	SSRC        uint32 `json:"ssrc"`
 	PayloadType uint8  `json:"payloadType"`
 }