New features:

- add and remove methods added to GeneralTaxonomy
- add, remove and change methods added to Python API
- weight-related methods added to Python API
- Python iteration faster and takes less memory
- test coverage increased to >90%.

See #16 for more details.

This consolidates our new Rust/Python taxonomy library from taxonomy-rs into the old taxonomy repo.

Initial release. Try to specify point releases in requirements.txt files for other modules/projects hereafter.