freetype + rusttype as font drawing libraries

[P-E-Meunier]

The quality of rusttype rendering, as well as the number of font formats available, makes it a little experimental for general-purpose use.

Is it be possible to use features to activate this in piston, (or have a feature to change it to freetype)?

[bvssvni]

Cargo features should not be interfering with each other, so this would require adding another module under a new feature flag. Currently, the graphics backends reexports the type, so it requires a custom override at application level to use the non-standard font library.