[webrtc-stats] new commits pushed by vr000m

The following commits were just pushed by vr000m to https://github.com/w3c/webrtc-stats:

* Fix a few IDL inconsistencies (#547)

* Make RTCTransceiverStats inherit from RTCStats

close #542

* Make dataChannelIdentifier an unsigned short

Same as the [definition of  in WebRTC](https://w3c.github.io/webrtc-pc/webrtc.html#dom-rtcdatachannel-id)
close #541

* Make RTCVideoSourceStats.framesPerSecond a double

as other definitions of framesPerSecond members in other stat objects
close #540

* Mark obsolete stats section as informative

This helps clarify the WebIDL fragments shouldn't be implemented and needs not be tested

* Hide long list of obsolete stats sections from table of content
  by Dominique Hazael-Massieux
https://github.com/w3c/webrtc-stats/commit/9c60a988b3fc34bb9e4c286cd9f7304c10129c95