in unit testing without display plots, the same figure would be used
over and over again. This is problematic when mixing 3D and 2D axes

- stencil plotting & transformation now in ps.stencil
- additional documentation & notebooks

- typos, more content
- added numba to benchmark comparison

This restructuring allows for easier separation of modules into
separate repositories later. Also, now pip install with repo url can be
used.

The setup.py files have also been updated to correctly reference each
other. Module versions are not extracted from git state