add fontsetter

[m4rc1e]

This module adds the ability to change font attributes from a yaml file e.g

fix.yaml:

OS/2->sTypoAscender: 1000
name->setName: ["Inter 4, 1, 3, 1, 0x409]

cli:

python -m gftools.fontsetter MavenPro[wght].ttf fix.yaml

It can also call functions on font tables. In the above example, we execute name.setName with the values being a list of arguments. The design is pretty generic so I wouldn't be surprised if it could work on .ufos as well with minimal tweaking.

My plan is to eventually add this to the gftools builder and gftools fix-font. Many people would argue that they'd prefer these modifications to be made to font sources only. However, many families have such as Inter don't follow our spec 1/1 so this module gives us the ability to cut our own release which conforms to our requirements.