Update to work on stable Rust aka. move to recent version of pyo3

[programmerjake]

There's a workaround branch for getting this to compile on recent compilers (work-around-const-fn-removal), but that isn't a very good way to get this to work...ideally algebraics would move to a recent version of pyo3, but that requires rewriting a major portion of the Python bindings due to pyo3 API changes.

See also: #1
Same issue on Debian Salsa