Brightway2

- FEATURE: New backend, sqlite, which is the default. Should massively reduce memory consumption in most cases, as entire databases don't need to be loaded.
- FEATURE: Backend now return activity and exchange proxies instead of raw data, making for easier manipulation and construction.

Note: Both packages `bw2search` and `bw2simple` are obsolete - their functionality is now included in `bw2data` by default.

Data cannot be directly migrated from bw2data < 2; instead, databases should be exported as BW2Package files and then re-imported.

* Fix [78](https://github.com/brightway-lca/brightway2-calc/issues/78): Allow for selective use of distributions or arrays depending on matrix label
* Fix [77](https://github.com/brightway-lca/brightway2-calc/issues/77): Prevent multiple `remap_inventory_dicts` calls
* Fix [71](https://github.com/brightway-lca/brightway2-calc/issues/71): Poor error message when no LCIA data is supplied
* Documentation improvements
* Switch packaging to `pyproject.toml`

Never happened, can't prove anything :)

* Packaging updates

* CI workflow updates
* Merge [65](https://github.com/brightway-lca/brightway2-calc/pull/65): Add PyPI and conda-forge badge
* Fix hidden dependency on `bw2data`

* Add some backwards compatiblity methods