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/routing/readwritesplit/readwritesplit.c

@@ -113,7 +113,7 @@ static bool create_backends(ROUTER_CLIENT_SES *rses, backend_ref_t** dest, int*
  *
  * @return The module object
  */
-MODULE_INFO *GetModuleObject()
+MODULE_INFO *MXS_CREATE_MODULE()
 {
     static ROUTER_OBJECT MyObject =
     {