Introduction of IXWebSocketSendData (#347)

* Introduction of IXWebSocketSendData that makes it possible to not only send std::string but also std::vector<char/uint8_t> and char* without copying them to a std::string first.

Add a sendUtf8Text() method that doesn't check for invalid UTF-8 characters. The caller must guarantee that the string only contains valid UTF-8 characters.

* Updated usage.md: sendUtf8Text() and IXWebSocketSendData

ixwebsocket/IXWebSocketPerMessageDeflateCodec.cpp

@@ -78,6 +78,12 @@ namespace ix
         return compressData(in, out);
     }
 
+    bool WebSocketPerMessageDeflateCompressor::compress(const IXWebSocketSendData& in,
+                                                        std::string& out)
+    {
+        return compressData(in, out);
+    }
+
     bool WebSocketPerMessageDeflateCompressor::compress(const std::string& in,
                                                         std::vector<uint8_t>& out)
     {