Convert most of it to python3.
Focus on algorithms.
Add some unittest using existing code.
Started migration to Numpy-style docstrings.
Hijacked Tree & PropertyTree classes (and related/necessary Exceptions & functions) from older `openalea.container` library in `tree` submodule.
Modern `pyproject.toml` approach.
Kept the old license, but probably need to change that.
Attempt to keep authorship and acknowledge it.

I still have to work on the GUI (PyQt4).
Move it to a `gui` submodule.