Codechange: Let the compile generate the master command table out of templated command traits.

This is using a non-intrusive type-traits like templated system, which
allows compile-time validation that the command table and the command
enum match up.

src/settings.cpp

@@ -44,6 +44,7 @@
 #include "newgrf_config.h"
 #include "fios.h"
 #include "fileio_func.h"
+#include "settings_cmd.h"
 
 #include "table/strings.h"