Introduce two helper macros

`TOGGLENUMLOCK` is the index of the macro, to be used in the `macroAction`
function, and `Key_ToggleNumlock` is to be used in the keymap, instead of
`M(0)`. This is considerably friendlier than before.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>

src/Keyboardio-LEDEffect-Numlock.h

@@ -4,6 +4,9 @@
 #include "Keyboardio-Macros.h"
 #include "LEDUtils.h"
 
+#define TOGGLENUMLOCK 0
+#define Key_ToggleNumlock M(TOGGLENUMLOCK)
+
 class NumLock_ : LEDMode {
  public:
   NumLock_ (void);