Simple-Web-Server Files

Various improvements and cleanups, most notably: * Fixed Client<HTTPS> proxy requests * Added client verification when a verify file is passed to Server<HTTPS> * Added session_id_context for session reuse * Server errors are now passed to an on_error std::function if set * Added crypto.hpp for convenient C++ wrappings for commonly used OpenSSL functions * Cleanup of server-constructors. Previous constructors have been marked as deprecated * Added on_upgrade std::function for cases where one wants to handle connection upgrades by another library, for instanace Simple-WebSocket-Server * Timeout can now be set for Client requests * Client now supports Connection: close * Added support for request header Connection: keep-alive in Server * Added Server::Request::parse_query_string()