* 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
