Additional fontmake tasks

Currently, fontmake let's us run ttfautohint

It'd be great if it could also:

- run psautohint
- take the CLI params of pyftsubset and call the fontTools.subset
- do basic font renaming
- optionally do "feature freezing" though I dunt think it's needed

If there were .DesignSpace lib keys to run a series of fontmake builds for different targets, all this could be controlled from .DesignSpace (which I think is the right place) and then a complete build could be done with

fontmake -m my.designspace