To achieve host-path backend routing, we changed behaviour of
--backend-http2-connections-per-worker.  It now sets the number of
HTTP/2 physical connections per pattern group if pattern is used in -b
option.

Fixes GH-292

There are many requests which changes its meaning when we rewrite
path.  This is due to bad percent-encoding in URI; reserved characters
are just used without percent encoding.  It seems this is common in ad
services, but I suspect more to come.  For reverse proxying situation,
sane service most likely encodes URI properly, so probably this is not
an issue.

If pattern ends with '/', and pattern and path matches without that
slash, we consider they match to deal with request to the directory
without trailing slash.  That is if pattern is "/foo/" and path is
"/foo", we consider they match.

-b option syntax is now <HOST>,<PORT>[;<PATTERN>[:...]].  The optional
<PATTERN>s specify the request host and path it is used for.  The
<PATTERN> can contain path, host + path or host.  The matching rule is
closely designed to ServeMux in Go programming language.

This commit fixes the bug that DATA is not consumed if
nghttp2_http_on_data_chunk is failed.  It also simplify the handling
of missing stream in NGHTTP2_IB_READ_DATA state.

This commit documents NGHTTP2_ERR_DATA_EXIST also occurs if HEADERS
has been already attached to stream too.  This commit also fixes
possible assertion error, and now nghttp2_submit_headers() and
nghttp2_submit_response() may return NGHTTP2_ERR_DATA_EXIST.  But we
recommend to use nghttp2_submit_request() and
nghttp2_submit_response(), and using them will avoid this error.

* fix build broken by recent changes
* place all build artifacts to OBJDIR
* explicitly add manifest (VC9/10)
* modernize python bindings creation
* some minor refactoring