Coldtype

Added
- Minor improvements to the self-rasterizing/drawbot-renderer, to support transparent backgrounds
Removed
- `drawbot_script` and `drawbot_animation` from the global import; now reside and can be imported from `coldtype.drawbot` module

Added
- `coldtype.fx.skia`
- `SkiaImage` (subclass of `DATImage`, which has been moved to `coldtype.img` module)
Removed
- `.phototype`/`.color_phototype` methods on `DATPen` — these are now "chainable" methods in the _coldtype.fx.skia_ module, and can be applied by importing ala `from coldtype.fx.skia import phototype` and then chaining to a pen, `.ch(phototype(...))`