The profiler and benchmarking showed that calling evbuffer_add()
repeatedly is very costly. To avoid this, we buffer up small writes
into one large chunk and call evbuffer_add() less times.

some small additions for clarity. please check to ensure meaning is preserved.

automake version is a bit picky about installation location and uses
different compiler flags from distutils. We prefer official distutils.
Now nghttp2.c, which is generated by cython, is distributed in
archive.

Doing inflation after error produces invalid results, especially, if
it is in NGHTTP2_HD_STATE_READ_INDEX, the inflater->left could be 0,
which causes assertion error.  Add sanity assertion for index

The statistics of pushed resources are also calculated.

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.

Add --enable-strict-http-parser mode to enable it.

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.