cube.make_cube_faces is now free of pointer arithmetic and can thus be marked as @safe
Added a tiny local commands function.
Game now saves selected block type on quit.
Removed unused files.
Removed unused things.
Refactor.

- Changed some ints to bools.
- x, y, z, rx, ry are now members of the struct Player, of which there is one global instance.
- Global int flying is now a bool member of Player.
- Entry -> Block
- Block.w -> Block.type
- Use Blocks enum instead of magic numbers.
- Map.data: Block* -> Block[]
Removed commented code.