Port TCOD layout to Unicode.

[HexDecimal]

I've been trying to ignore it, but it's pretty clear that the TCOD layout will need to be converted into Unicode before I can even think of removing it.

• Invert the TCOD layout codec so that maps tiles to codepoints, instead of the other way around.
• Add a TCOD to Unicode mapping, TCOD_chars_t could be used as a reference.
• Deprecate TCOD_chars_t, just updating it to Unicode would be too limiting.

This should help with #51 and any other updates to the printing functions.