Create an answer with apparently the right number of m-lines. Would be nice if there were tests for it
Checkpoint on SetLocal(Answer)
More line numbery goodness
And put the line number in the error log, too
Start of actually emitting the tracks
Merge pull request #84 from adamroach/sdp

More line numbery goodness
Merge pull request #86 from ekr/MS_create_answer1

Ms create answer1
Short circuit properly, and remove some outdated comments.
fmtp support, make some loops safer, and add some useful asserts to the
unit test.