Support characters outside of ASCII

Currently we just support ASCII characters, loading the needed tiles into memory when the UI is initialized. However, I think it might be possible to support more characters by dynamically loading in the tiles for characters as they are needed.

The font used right now is `font8x8_basic`. However, there are actually more characters available in `font8x8`, or perhaps something like [Unifont](https://www.unifoundry.com/unifont/index.html) would be feasible, if we really want to support *everything*. [Unscii](https://github.com/viznut/unscii) is also an option for staying 8x8, but I'm not sure how much more coverage we really get with it vs font8x8.