Migrate to pyo3 0.13

[Johann Tuffe]

First thank you for the crate, works like a charm!

Do you plan to upgrade it to pyo3 0.13? Not very important but it would clear my dependency trees for projects which have migrated.

[Michal 'vorner' Vaner]

Hello. I wasn't watching it, so I didn't know about the new release. Yes, I generally want to keep this up to date.

Do you want to give the branch a try before I release it? #6

[Johann Tuffe]

Thanks!
I confirm it seems to be working fine

[Michal 'vorner' Vaner]

Great, I've just released it to crates.io.