Font features: OpenType support, multiple styles about havoc

[ii8]

Supporting multiple styles should be fairly easy, some small modifications to glyph.c so multiple font objects can be created (I was lazy so it just uses static memory atm.)
And then just using a different font object in the draw_cell function depending on the attributes. That would do it for bold, some extra stuff might have to be figured out for italic.

To support OpenType would probably mean to start depending on FreeType or something similar. FreeType would give support for all sorts of font formats but also a lot of features we really don't need or care about in monospaced termnials. So originally I didn't use it because of lofty minimalism goals(few dependencies, small static binary etc.)