Also updates docs

Currently, nghttpd server only compresses files whose extensions are
one of .html, .js, .css and .txt.  nghttp advertises its support of
per-frame compression in SETTINGS frame.  To implement this feature,
we added 2 public API: nghttp2_session_get_remote_settings() and
nghttp2_gzip_inflate_finished().

This allows users of OS X 10.9 to run nghttpd (and friends) with
threading entirely disabled, to avoid crashes on startup related to
std::mutex.

libevent-server.c:552:43: error: missing field 'recv_callback' initializer [-Werror,-Wmissing-field-initializers]

libevent-client.c:355:43: error: missing field 'recv_callback' initializer [-Werror,-Wmissing-field-initializers]

libevent-server.c:691:8: error: C++ style comments are not allowed in ISO C90

nghttp2_session.c:1615:9: error: C++ style comments are not allowed in ISO C90 [-Werror]

nghttp2_stream.h:94:43: error: comma at end of enumerator list [-Werror=pedantic]

nghttp2_hd.h:115:30: error: comma at end of enumerator list [-Werror=pedantic]

nghttp2_int.h:50:33: error: comma at end of enumerator list [-Werror=pedantic]

referred to by the global variable 'long_options' upon returning to the caller.
This will be a dangling reference

Found by Clang Analyzer