Upgrade to newer PyO3.

[m-ou-se]

We're stuck at PyO3 0.11 because PyO3/pyo3#1143 breaks wrap_pyfunction!() for us. See PyO3/pyo3#1597

Once that fix is merged and published, we can update to the latest PyO3 again.

[jam1garner]

@m-ou-se I believe this is fixed by 2506a36?

[m-ou-se]

Yes, thanks!