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

rtcrtpdecodingparameters.go

@@ -1,8 +1,8 @@
 package webrtc
 
-// RTCRtpDecodingParameters provides information relating to both encoding and decoding.
+// RTPDecodingParameters provides information relating to both encoding and decoding.
 // This is a subset of the RFC since Pion WebRTC doesn't implement decoding itself
 // http://draft.ortc.org/#dom-rtcrtpdecodingparameters
-type RTCRtpDecodingParameters struct {
-	RTCRtpCodingParameters
+type RTPDecodingParameters struct {
+	RTPCodingParameters
 }