tileset WIP

Work in progress.

- the 8x8 ASCII mode is now sprite-based and looking cute. This
overrides standard colors.
- Then I decided to port over this tiled 8x8 to 16x16, so I doubled the
sprites.
- You can switch while in 16x16 map mode by pressing "w". It only swaps
player, monsters and doors.

TO DO
- Eventually, I'll keep in 16x16 the two tile modes, while the sprites
will stay fixed.
- In 8x8 I'll try to switch between ASCII and graphic.

Comments:
- Added globals at the beginning to assign names to both converted 8x8
tiles (t28), and 16x16 (t16). I then swap those in the keyboard lookup,
by using in function an "universal" name (u16).