[fontgen] upgrade to python3 and make it easier to use

[cdluminate]

Debian has upgraded it's fontforge python version to 3.X . So in the next update we will be able to get rid of python2.

As discussed previously, this tool should be reworked to make it easier to use. Apart from the code cleanups and refactoring. I'm going to build a pipeline using the following dataset so users can build custom font with a single command.
https://www.kaggle.com/c/tiny-imagenet/data

Please assign this issue to me.
(I'm recently preparing for examinations and other things, still need some time to actually implement it)

[hpjansson]

Sorry, forgot to assign this back in April. Hope the exams went well!

You should be able to assign issues to yourself now, let me know if you need anything else from me. Feel free to create a feature branch for it; then we can rebase-merge it (preserving history) when you think it's ready.

[cdluminate]

I'm marking this issue as resolved in advance. See #128

[hpjansson]

Brilliant!