nghttp2 v1.12.0

• Add nghttp2_session_set_local_window_size API function
• Add nghttp2_option_set_max_send_header_block_length API function (GH-613)
• Fix warning: declaration of 'free' shadows a global declaration (Patch from Alexis La Goutte)
• examples: Add ALPN support to tutorial client/server (GH-614)
• nghttpx: Reduce TTFB with large number of incoming connections
• nghttpx: Rewrite read timer handling
• nghttpx: Clean up neverbleed AF_UNIX socket
• nghttpx: Add --backend-max-backoff option
• nghttpx: Use 16KiB buffer for reading to match TLS record size
• nghttpx: Add healthmon parameter to -f option to enable health monitor mode
• nghttpx: Receive reference of std::mt19937, not making a copy
• nghttpx: Fix bug that backend never return to online (GH-615)
• nghttpx: Implement client IP based session affinity
• nghttpx: Add --api-max-request-body option to set maximum API request body size
• nghttpx: Add api parameter to --frontend option to mark API endpoint
• h2load: Add content-length header field for HTTP/2 and SPDY as well
• h2load: Implement HTTP/1 upload (GH-611)