Renamed spdylay_req_submit and spdylay_reply_submit as spdylay_submit_request and spdylay_submit_response

Check stream before sending SYN_REPLY and DATA. Don't make stream if incoming SYN_STREAM has FIN and UNIDIRECTIONAL set.

This example program can connect to remote host given in command-line
via SSL and retrieves given path using SPDY protocol.
To build this program, OpenSSL + NPN support is required.

Use stream->pri for priority of SYN_REPLY.

Fixed bug that Z_DATA_ERROR is not handled.
Fixed bug that spdylay_frame_alloc_pack_nv does not use nv_offset correctly.

Now recv_callback and send_callback accepts session argument.
spdylay_session_free was also renamed as spdylay_session_del.