Use (void) for function prototypes with no parameters

This is required when compiling these headers as C code. These were
omitted becuase before the addition of examples these headers were
only compiled locally as C++ files where adding the void keyword is
not needed.

include/SFML/Network/UdpSocket.h

@@ -203,7 +203,7 @@ CSFML_NETWORK_API sfSocketStatus sfUdpSocket_receivePacket(sfUdpSocket* socket,
 /// \return The maximum size of a UDP datagram (message)
 ///
 ////////////////////////////////////////////////////////////
-CSFML_NETWORK_API unsigned int sfUdpSocket_maxDatagramSize();
+CSFML_NETWORK_API unsigned int sfUdpSocket_maxDatagramSize(void);
 
 
 #endif // SFML_UDPSOCKET_H