Previously h2load supports SPDY only for https URI.  This is because
SPDY has no mechanism to negotiate its protocol version without NPN.
With this change, user can specify the exact protocol version to use
when http URI (without SSL/TLS) is used.

It seems that setup.py gets deleted before python executes it in
clean-local.  To prevent this situation, we just use .NOTPARALLEL.

Previously we distribute nghttp2.c in python, which is cythonized C
source code from nghttp2.pyx.  Since it is distributed in archive it
exists in source directory.  But we use python distutils which
operates in build directory and does not support C source files in out
of tree directory (i.e., not under the build directory).  Copying C
source file to build directory is a bit dirty, so we just decided not
to ship nghttp2.c.

nghttp2_submit_{headers,request}: Return NGHTTP2_ERR_INVAILD_ARGUMENT
if pri_spec->type is invalid.

nghttp2_submit_push_promise: Return NGHTTP2_ERR_PROTO if issued by
client.

nghttp2_submit_altsvc: Return NGHTTP2_ERR_PROTO instead of
NGHTTP2_ERR_INVALID_STATE if issued by client.

Patch from Gisle Vanem

"""
I tried to build this extension on Windows, but failed since
ws2_32.lib is needed in libraries
"""

Replace int *eof with uint32_t *data_flags so that we can easily
extend functionality if we have to (but we don't do if possible).

To make adding new option easier, we decided to make the details of
option struct private and hide it from public API.  We provide
functions to set individual option value.