implement list_fonts::list_families
implement list_fonts::list_families

A list of families is returned. Each variant contains the variant's
style, the filepath for the variant, and the index of the variant in the
file. This info should be enough to get freetype to actually load a
font.

alacritty/alacritty,dannydulai/alacritty,alacritty/alacritty,jwilm/alacritty,dannydulai/alacritty,jwilm/alacritty,jwilm/alacritty,jwilm/alacritty