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/monitor/mysqlmon/mysql_mon.c

@@ -94,7 +94,7 @@ static const char* hb_table_name = "maxscale_schema.replication_heartbeat";
  *
  * @return The module object
  */
-MODULE_INFO* GetModuleObject()
+MODULE_INFO* MXS_CREATE_MODULE()
 {
     MXS_NOTICE("Initialise the MySQL Monitor module.");