Use enums for sound effects

This adds an anonymous enum for sound effects and replaces all calls to
music.playef that use integer literals.

This is not a named enum (that can be used for strict typechecking)
because sound effect IDs are essentially part of the API of the game -
many custom levels use these numbers. This is just to make the source
code more readable without needing a comment to denote what number is
what sound.

desktop_version/src/KeyPoll.cpp

@@ -172,7 +172,7 @@ void KeyPoll::Poll(void)
             {
                 /* Reload language files */
                 loc::loadtext(false);
-                music.playef(4);
+                music.playef(Sound_COIN);
             }
 
             BUTTONGLYPHS_keyboard_set_active(true);