This makes the buildsystem forward compatible with automake>=1.14 since
nghttp uses a recursive build. It avoids a large and non-scary warning
on running autoreconf, summarized as:

src/Makefile.am:57: warning: source file 'http-parser/http_parser.c' is in a subdirectory,
src/Makefile.am:57: but option 'subdir-objects' is disabled

Just to make it easier to find the info.

The encoder algorithm is simplified and it now preserves ordering
of the headers. It also becomes one-pass encoder.

This returns run-time information about the lib

warning: comma at end of enumerator list [-Werror=pedantic]

Since the name of the file is 'libnghttp2*' I think we should use the
full name within it as well (for the Name: field), as it gets confusing
otherwise for users and for pkg-config.

Also, 'Requires.private' breaks pkg-config's ability to extract -I etc
from the Cflags below it. I believe it should be 'Libs.private' and the
right side should then list the libs with -l.

With these changes, I've successfully written a configure script to
find and use libnghttp2.

We call on_stream_close_callback even if stream->state is
NGHTTP2_STREAM_INITIAL. This will happen while sending request
HEADERS, a local endpoint receives RST_STREAM for that
stream. It may be PROTOCOL_ERROR, but without notifying stream
closure will hang the stream in a local endpoint.

Also the comment referred to non-existing SPDY defines

Use --dh-param-file option to specify a file including DH parameters
in PEM format.

For example, you can create DH parameters with 1024 bit key using
following command:

$ openssl dhparam -outform PEM -out dhparam.pem 1024