Create a macro for module declarations

The modules are now declared with a common macro. This allows future
additions to the module loading process while also making the loaded
symbol name a constant.

server/modules/protocol/testprotocol/testprotocol.c

@@ -52,7 +52,7 @@ static int test_connection_limit(DCB *dcb, int limit){return 0;}
  *
  * @return The module object
  */
-MODULE_INFO* GetModuleObject()
+MODULE_INFO* MXS_CREATE_MODULE()
 {
     static GWPROTOCOL MyObject =
     {