Fix several issues identified in draft review; update references

sctp-sdp and trickle-ice moved to WG drafts
msid-semantic added
UDP/TLS/RTP/SAVPF
a=ssrc and cname attribute
a=sctpmap stuff
Ordering of m= section generation
Unique m= section ports
s=- session name
Rules for o= when SDP changes
Fix fat fingering
Change to -05
Update timestamp; update requirements section, fix typos, move call flows to examples section.

Update timestamp to today.
SDP requirements section has been split into "mandatory to implement"
and "mandatory to use".
SDP call flow examples moved to the examples section.
Fixed several typos discovered while proofreading.
Remove some [OPEN ISSUE]s that have been resolved.
Move to -06 version of draft
Fix confusing text on pranswers and session-level attrs

Rewrite section on pranswer handing to make clear what the drawbacks of
pranswer are.
rebase to new master
Merge branch 'cj-pool1' of github.com:juberti/jsep into cj-pool1