When deciding whether to close the client connection, check
request_connection_close_ of Downstream in addition of
response_connection_close_. Also we only add "Connection: Keep-Alive"
header to the HTTP/1.0 or HTTP/0.9 clients.

github translates "Client/Server" in section header to "#clientserver"
fragment, but if it is referred by `Client/Server`_, it is translated
into "#client-server". It is best to avoid '/' in section header.

We use intrusive style pattern in spdylay_stream, which now has
spdylay_map_entry has its first member.

In practice, Session.resume_data() will be used without checking there
is deferred data or not. Actually, there is no API to check this.  So
it is better not to raise exception. Instead return False to notify
error. If the method succeeds, it returns True.

When --enable-src is given, the programs in src directory will be
built. If --disable-src is given, those programs will not be built. If
none of them are given, --enable-src is assumed.

To distinguish the to-be-installed programs and non-installable
example source code, the former programs, spdycat, spdydyd and shrpx,
were moved to src directory. spdynative was removed from Makefile
because it does not appeal to any users much.

get_npn_protocols() is high level wrapper for
spdylay_npn_get_proto_list() and the returned list can be passed to
ssl.SSLContext.set_npn_protocols().

spdylay_npn_get_proto_list() returns a pointer to the supported SPDY
version list. The element of the list is spdylay_npn_proto struct. It
contains all SPDY version information this library supports. The
application can use this information to configure NPN protocol
offerings/selection.

ssl socket and ssctrl are also instance variable now.