Extend Buffer with new methods ans assertions.
Add read() and write() methods to UdpMulticastSocket.
Add default constructor for Buffer class.
Assure (using assertions) that Buffer::get_date() will not return null.
Register UdpMulticastSocket in main loop in constructor.
"offset" parameter on UspMulticastScoket::write() is 0 by default.
Test for UdpMulticastScoket added.
Update Makefiles.