Issue70 profile names2

I just rewrote this. 
This probably could be explained a bit more, e.g.:

The use of AVPF or AVP simply controls the timing rules used for RTCP feedback. If AVPF is provided, or an "a=rtcp-fb" attribute is present, assume AVPF timing, i.e. a default value of "trr-int=0". Otherwise, assume AVP timing, and a default value of "trr-int=4".