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/IXWebSocketPerMessageDeflate.cpp

@@ -78,6 +78,11 @@ namespace ix
                _decompressor->init(inflateBits, clientNoContextTakeover);
     }
 
+    bool WebSocketPerMessageDeflate::compress(const IXWebSocketSendData& in, std::string& out)
+    {
+        return _compressor->compress(in, out);
+    }
+
     bool WebSocketPerMessageDeflate::compress(const std::string& in, std::string& out)
     {
         return _compressor->compress(in, out);