Port to Python 3

[abompard]

This changeset ports the codebase to Python 3. It is not Python2-compatible.

Fixes: #75

[jwilner]

Hi @abompard -- thanks for the PR.

We'd like to land it but are going to need spend some time reviewing and testing it.

Along those lines, I'd like to know your impression of this change set.

• Is it complete in your opinion?
• Are you using it in production?
• Have you hit any issues?

Thanks again!

[daks]

Hi, just a message to tell you @abompard and @jwilner that we integrated this code and use it successfully on Debian Bullseye 11 with Python 3 (3.9.2)

We use it with the patch from #69 which we already used on previous py2 version.