Bw-processing

* Add support for parquet files

* Switch versioning scheme to help WASM packaging

* Packaging fixes

* Change distribution name to fix Windows installation issues (`bw-processing` instead of `bw_processing`)
* Change packaging to [our common standard](https://github.com/brightway-lca/cookiecutter-brightwaylib)

* Don't export DataFrame index columns

* Add `simple_graph` convenience function