The internal OverpassNumbersFont is generated from `overpass-numbers.xcf`. This contains
text using the provided font. `overpass-numbers.png` is an export of this file.
`overpass-numbers.raw` is generated using `convert overpass-numbers.png -depth 1 gray:overpass-numbers.raw`.
`../src/font.rs` contains a mapping for each character and the size of the
characters.