Upgrade pion/webrtc from v2 to v3

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

examples/rtp/main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"math/rand"
 	"net"
 	"os"
 
@@ -51,7 +52,7 @@ func main() {
 	videoTrack := mediaStream.GetVideoTracks()[0]
 	defer videoTrack.Close()
 
-	rtpReader, err := videoTrack.NewRTPReader(x264Params.RTPCodec().Name, mtu)
+	rtpReader, err := videoTrack.NewRTPReader(x264Params.RTPCodec().MimeType, rand.Uint32(), mtu)
 	must(err)
 
 	addr, err := net.ResolveUDPAddr("udp", dest)