This change implements spdylay_map functions in iterative approach
instead of original recursive approach. The iterative version is
overall faster than recursive one. The traversal function
(spdylay_map_each) is slightly slower but it is not noticeable.
Now remote and local settings are stored separately.
The initial window size is included in SETTINGS frame, all active stream's
window sizes are now updated.
Removed the initial_window_size member from spdylay_stream because
it is the same as remote_settings's initial window size.
