User can change file name using --mime-types-file option.

It seems that using ev_feed_event to signal write operation is much
faster than starting watcher.  This is probably due to the fact that
we don't need to wait in event loop.  The same thing cannot be done in
HTTP/2 frontend, since this will raise write operation for each stream
HEADER/DATA write, which leads to very small packets, hurting
performance.  Interestingly, HTTP/1 frontend also suffers the same
performance hit.

Revert "add PIDFile directive to systemd service"

h2load: do not overwrite protocol value

This reverts commit 19c095a8.

See discussion at #375 for details.

This commit also fixes the problem that application protocol is not
shown if cleartext spdy is used.

Update doc for Debian 7.0 or above and add g++ requirement

The encoder is not required to send dynamic table size update if the
table size is not changed from the previous value after accepting new
maximum value.

This will improve performance since we can avoid indirect call of
internal functions.  The downside is we now require libnghttp2 static
library to run unit tests.

Merge branch 'nghttpx-tls-dyn-rec-config' of https://github.com/LPardue/nghttp2 into LPardue-nghttpx-tls-dyn-rec-config