feature request: add `fonttools diff` to compare fonts with ttx

I often find myself using ttx in combination with some diffing tool, so much that I wrote a ttdiff shell function that takes two fonts (and optionally a list of table tags), and redirect the output of ttx to diff (pipes it to colordiff to get nice colors and less for pagination):

https://gist.github.com/anthrotype/6c3dce176314ec6ffb116b0f8561bee0

I guess many of us have their own variant of this. So I wonder, should we add a new sub-command, fonttools diff that uses python to do the same, so it works everywhere fonttools work and not just in a unix shell?

I think this is a nice first-time-contributor kind of PR. Any takers?

[justvanrossum]

In the meantime https://pypi.org/project/fdiff/ was made by @chrissimpkins, it’s awesome!

[behdad]

I’ll leave it to Cosimo, others, to figure out.