Release 2.7.0

• Allow Content-Enconding header with ulfius_send_http_request to compress the response body
• Add http_compression callback example
• Add static_compressed_inmemory_website callback example
• Add callback return value U_CALLBACK_IGNORE to igore incrementation of request->callback_position
• Add ulfius_add_websocket_extension_message_perform and ulfius_add_websocket_client_extension_message_perform for advanced websocket extensions management
• Add Compression Extensions for WebSocket
• Fix lots of websocket bugs thanks to Autobahn|Testsuite.