Add more unit tests for dungeon functions.
Add more unit tests for dungeon functions.

New tests for:

    `dungeon_add_area()`
    `dungeon_is_box_excavated()`
    `dungeon_alloc_tiles_for_box()`
    `dungeon_tile_at()`

donmccaughey/FiendsAndFortune,donmccaughey/FiendsAndFortune,donmccaughey/FiendsAndFortune