Merge pull request #88 from docfaraday/multistream_unit_tests

Multistream unit tests
Export a trivial description of the negotiated track pairs
Merge pull request #89 from ekr/MS_more_call_setup

Export a trivial description of the negotiated track pairs
First test with the full JSEP interaction
Merge pull request #90 from ekr/MS_full_call_setup

First test with the full JSEP interaction
Fix bug where we would load 0 length lists for various attributes, a bug
where we would load bogus rtpmap attributes for every payload type on
the m-line when no rtpmap attr existed, and fix a unit-test to squelch a
warning.