As suggested in GH-674

This commit also fixes the bug that SETTINGS timer continues after
connection was closed.

This script prints out the commit author from `git log` output.  Used
to update AUTHORS file.

2 APIs are added.  nghttp2_session_get_local_window_size() returns the
amount of data that the remote endpoint can send without receiving
connection level WINDOW_UPDATE.
nghttp2_session_get_stream_local_window_size() returns the amount of
data that the remote endpoint can send without receiving stream level
WINDOW_UPDATE.