Escape access log

src: BoringSSL supports SSL_CTX_set_{min,max}_proto_version.

The certain characters coming from client are now escaped with "\xNN"
where NN is the ascii code of the character in hex notation.

Signed-off-by: Piotr Sikora <piotrsikora@google.com>

asio: client: Send PING after 30 seconds idle

This reverts commit f69b52b1.

Instead use (void)VAR for better compiler compatibility.

This commit fixes the bug in nghttp2_session_want_write.  Previously,
it may return 0 if there is pending frames after GOAWAY frame is
submitted.

To avoid the situation that nghttp2_session_want_write keeps returning
nonzero after GOAWAY and the number of active streams is 0 (e.g., keep
receiving SETTINGS or PING), nghttp2_session_mem_recv now just
swallows the input data without parsing in this case.

nghttpx: Enable backend pattern matching with http2-proxy

.. after fork but before execv in multithreaded process.