Unicode support

[davidjoffe]

FYI:

(New unstable dev branch feature-unicode I'm using to play around with possible basic Unicode and TTF support in parts of the game :) )

(This is DISABLED currently by default as it's still in dev, but can be turned on with an optino in the Makefile (and/or config.h) but note would introduce two new dependencies: sdlttf and utf8proc so be aware if you start turning it on for any downstream ports etc.)

#148 (comment)

https://user-images.githubusercontent.com/7451578/203873317-415a834a-615e-46f3-821d-13bfb413b2a5.png