Ausankey

* Add `value_loc` option to control printing
of numeric values of flows. Several accompanying
options control the typesetting, etc.
* Add `label_duplicate` option to avoid printing
redundant labels.
* Add `other_thresh_XX` options to allow
recategorisation of entries with values below a
certain threshold.
* Add `sort_dict` option to override sort order for
individual labels.
* Internal code changes using OOP methods to
tidy up.

* Label alignment bug fix (not sure how it slipped through).
* Fixing it involved some nice tidy-up of the code.
* Took the opportunity to flesh out the documentation a little.

* Many more configuration options. (E.g., edges around flows/nodes, transparency of nodes, properties of label and title text, alignment of labels, …)
* Now allows flows that start and stop (which work with sorting).
* Reference documentation added to supplement the user documentation.
* Some breaking changes but no-one is using this besides me, right?

* Change package name from `auSankey` to `ausankey` to match Python standards
* All `mixedCase` options converted to `snake_case`
* Package management updated to `pypackage.toml` and build system now uses `hatch`
* Repository tidied up

* Initial release