python: Return Handler object for pushed resource from BaseRequestHandler.push

Also update doc
doc: Add Python API doc
Add HPACK deflation API
src: Use gmtime_r instead of gmtime
src: Eliminate use of snprintf
src: Rewrite util::format_hex
src: Use C++ style comments for C++ source code
Update doc
Update doc
Update nghttp and nghttpd example output
nghttpx: Remove Connection: close header field from CONNECT response

It appears that some Android client does not like Connection: close in
200 CONNECT response.  Browsers fine with this header field.  It is
better to remove it.  Squid does not emit it too.
Update http-parser to 8d9e5db981b623fffc93657abacdc80270cbee58
Update sphinx_rtd_theme to 54a48b1726ed602c9b5416ee46c639462ec315fe
nghttpx: Minor tweak to buffer size

Simplified when to send WINDOW_UPDATE to the backend, that is we send
WINDOW_UPDATE when input buffer is empty.
Remove useless debug code in nghttp2_stream_roots_add()
Take into account that pending_local_max_concurrent_stream could be too large

pending_local_max_concurrent_stream is, once local settings applied,
becomes NGHTTP2_INITIAL_MAX_CONCURRENT_STREAMS, which is very large
number.  When adjusting number of streams, we have to take min of
local effective SETTINGS_MAX_CONCURRENT_STREAMS and pending one.
Bump up version number to 0.4.0, LT revision to 3:0:0
Update man pages
Bump up version number to 0.5.0-DEV
Update doc