`rusttype` dependency is unmaintained, consider migrating to `ab_glyph`

[ciuncan]

Below RUSTSEC advisory come up with cargo audit for rusttype being a transitive dependency of this imageproc crate.
https://rustsec.org/advisories/RUSTSEC-2021-0140.html

There in the advisory, it mentions the alternative crate ab_glyph which started as fork of rusttype and has slight performance increase, too.