- BREAKING: Drop Python 3.7 support (EoL 2023-06-27).
- `Tree.save()` accepts a `compression` argument that will enable compression.
`Tree.load()` can detect if the input file has a compression header and will
decompress transparently.
- New traversal methods `LEVEL_ORDER`, `LEVEL_ORDER_RTL`, `ZIGZAG`, `ZIGZAG_RTL`.
- New compact connector styles `'lines32c'`, `'round43c'`, ...
- Save as mermaid flow diagram.