Add Mt. Moon Crater

The map functions and the ROM builds. It has no wild data, and nothing goes to it.

What's done;
- Map design, I think this is one of the best I've ever done, especially within these limits.
- Integration, set up a warp and you can go there, easy.

What's not done
- Wild data
- Fishing group
- Water mons
- Event signs
- Young Sada in Pewter Museum of Science

Very simple map to produce.

constants/map_constants.asm

@@ -136,7 +136,7 @@ DEF FIRST_INDOOR_MAP EQU const_value
 	mapconst FARAWAY_ISLAND_OUTSIDE,       18,  15 ; $72	- Was UNUSED_MAP_72
 	mapconst FARAWAY_ISLAND_INSIDE,        11,  15 ; $73	- Was UNUSED_MAP_73
 	mapconst POKEMON_MANSION_B2F,          12,  15 ; $74	- Was UNUSED_MAP_74
-	mapconst UNUSED_MAP_75,                  0,  0 ; $75	- Unused
+	mapconst MT_MOON_CRATER,                  25,  25 ; $75	- Was UNUSED_MAP_75
 	mapconst HALL_OF_FAME,                   4,  5 ; $76
 	mapconst UNDERGROUND_PATH_NORTH_SOUTH,  24,  4 ; $77
 	mapconst CHAMPIONS_ROOM,                 4,  4 ; $78