clang + libc++ does not work, it still requires libc++_shared.so
runtime even if -lstdc++ is used, which supposed to link with static
version of libc++.

It was markdown, we should use reST.

Previously, we didn't retry request on connection failure.  Sometimes
we hit the edge case where connection is about to lost just when we
write request.  To avoid this situation, we now retry request to
failed attempt.  We also add ConnectBlocker to MemcachedConnection not
to attempt to connect to memcached if connection could not be made
previously.

We use technique described in https://github.com/RJ/ketama

We use https://tools.ietf.org/html/draft-kazuho-h2-cache-digest-01 as
specification.  We haven't implemented flags handling yet.

We define the behaviour when NGHTTP2_ERR_CANCEL is returned from
before_frame_send_callback.  That is to cancel the frame passed to the
callback.

In our use case, x and y is quite small, and there is no chance for
overflow, and y is always integer.