Recent Numpy version do not support conversion from arbitrary iterables

otherwise the index gets lost

uses new Field.neighbor_vector

Markus Holzer authored Aug 02, 2019 and Markus Holzer committed Aug 06, 2019

derive gradient weights of other direction with
already calculated weights of one direction
via rotation and apply them to a field.

as_matrix gives now a deprecated warning and as_array is no newly implemented to replace it. as_array works with MutableDenseNDimArray now instead of Matrix

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

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