Adding error code for exceeding MAX_CONCURRENT_STREAMS
Adding option to use REFUSED_STREAM
Splits either in send+recv.
Tweaks diagram.
Merge pull request #659 from hruellan/diagram

Replaces either with send+recv
Merge pull request #652 from http2/mcs_err2

Options for SETTINGS_MAX_CONCURRENT_STREAMS violations
Prepare for release
Fix typo (s/sever/server/)