Rewrite TagBot in Julia (long-term goal)

Currently, TagBot is written in Python.

It would be great to eventually rewrite TagBot in pure Julia, for the following reasons:
- We might as well "eat our own dog food" when developing our own tools.
- It is always great to showcase the use of Julia as a general purpose programming language (as opposed to just a scientific computing language).

I don't have the time right to do this, and I'm guessing that @christopher-dG doesn't either. But I figure we leave this issue open (maybe label it as `Help Wanted`), and eventually maybe someone will do it.