nghttp2_session_mem_send tiny doc fix

Patch from Dave Beckett
nghttpx: Fix priority bits
nghttpx: Fix typo
nghttpx: Code cleanup
nghttp: Use nghttp2_session_mem_recv and nghttp2_session_mem_send
nghttpd: Use nghttp2_session_mem_recv and nghttp2_session_mem_send
examples: Check stream_data is null
nghttpx: Initialize response_htp_ with 0
Strict handling of max concurrent streams

Exceeding ACKed max concurrent streams results in connection error.
This change fixes the bug that num_{incoming,outgoing}_streams
is decremented wrongly if a stream is in reserved state and
RST_STREAM is send and its state is changed to NGHTTP2_STREAM_CLOSING.
This change also fixes the bug that transmission of push response
HEADERS does not increase num_outgoing_streams.
Code cleanup
Rename --enable-maintainer-mode configure option as --enable-werror
Add --enable-debug configure option to define DEBUGBUILD macro
src: Disable strip http-parser mode

Add --enable-strict-http-parser mode to enable it.
Add test to verify that deflater can handle initial buf smaller than default
Remove END_PUSH_PROMISE in favor of END_HEADERS
Update doc
Revert 6c51bd09791ba6f547a90d575af681510ee3d52d
nghttpx: Code cleanup
Add promised_stream_user_data parameter to nghttp2_submit_push_promise

This is very useful to associate application specific data to promised
stream.

nghttp2_nv_array_copy now does not complain the header field is large.
nghttp: Wait for pushed resources to complete

The statistics of pushed resources are also calculated.