Changes as described by issues below

Support for control of quality, resolution, framerate and layering added, as described in https://github.com/openpeer/ortc/issues/31
RTCRtpListener object added and figure in Section 1 updated, as described in openpeer#32
More complete support for RTP and Codec Parameters added, as described in openpeer#33
Data Channel transport problem fixed, as described in openpeer#34
Various NITs fixed, as described in openpeer#37
Section 2.2 and 2.3 issues fixed, as described in openpeer#38
Default values of some dictionary attributes added, to partially address the issue described in openpeer#39
Support for ICE TCP added, as described in openpeer#41
Fixed issue with sequences as attributes, as described in openpeer#43
Fix for issues with onlocalcandidate, as described in openpeer#44
Initial stab at a Stats API, as requested in openpeer#46
Added support for ICE gather policy, as described in openpeer#47

- merge pull request from SteveALee