Fixes font raster for mono, gray bitmaps (#590)
Fixes font raster for mono, gray bitmaps (#590)

As it turns out, FreeType does not always provide glyph data in LCD mode
as we requested. We now correctly handle several common modes returned
from FreeType including Lcd, Mono, and Gray.

Note that we don't check number of grays at this time since it's

1. Almost always 256, according to FreeType docs
2. Not available in the Rust FreeType bindings being used

Resolves #515
Resolves #185
Resolves #482
jwilm/alacritty,alacritty/alacritty,alacritty/alacritty,jwilm/alacritty,jwilm/alacritty,jwilm/alacritty