We should only call daemon() after ListenHandler is
instantiated, where  SSL_CTX_use_PrivateKey_file is called,
otherwise we have no stdin/stdout to get the password for
keyfile.

We should probably make this spec file a template and integrate
it with our build process (make package?). Will follow-up with
that eventually.

This change implements spdylay_map functions in iterative approach
instead of original recursive approach. The iterative version is
overall faster than recursive one. The traversal function
(spdylay_map_each) is slightly slower but it is not noticeable.

The reason why we choose SPDY/2 as default for SPDY prxy was due to
Chrome's window update bug. Now its fix is available in Chrome stable,
we make SPDY/3 as default.

We cannot use assert(stream_user_data) because server-pushed stream
does not have stream_user_data.

The on_ctrl_not_send_callback, on_ctrl_recv_parse_error_callback and
on_unknown_ctrl_recv_callback were added. The latter 2 callbacks are
purely debugging purpose.  In on_ctrl_not_send_callback, If sending
SYN_REPLY failed, issue RST_STREAM to avoid a stream hanging around.

If resultant length of a frame exceeds the maximum value (which is
2**24 - 1 for SPDY/2 and 3), SPDYLAY_ERR_FRAME_TOO_LARGE is used to
indicate this error. This error will be notified by
on_ctrl_not_send_callback.

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.