usability and functionality:
- implement `breakdown()` for discourseme constellations
- make `Corpus.query()` the central entrypoint (also for s-attribute queries)
- remove inplace subcorpus creation; return new `Corpus` instead
stability and compatibility:
- make pandas operations future-proof
- catch decode errors and missing s-attributes
misc:
- simplify README and introduce Vignette
- update github workflows (include python 3.10; simplify publishing)
- work towards PEP compliance