- `supervenn()` now returns a SupervennPlot object with attributes
- chunks can be inspected via the `.chunks` attribute and `.get_chunk` method
- default random seeds count is increased from 1000 to 10000 (1000 was probably a typo)
- some refactoring in `_algorithms`
- fixed typo in `chunks_ordering` parameter option: `'occurence'` to `'occurrence'` (old version is still supported, but a warning is raised)