this to your children or students)

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

- update waLBerla package in order to make use of this function!

- new functions to easily extract stencil coefficients and visualize them
- Moved stencil functions from lbmpy to pystencils

- new time loop caches all kernel functions with their argument dict
  -> inner loop just calls C functions with cached kwargs

- updates in lbmpy benchmark
-> enables better numa placement

- support aligned load/stores
- nontemporal stores
- aligned memory allocation for arrays and temporary buffers

- removed warnings
- added flake8 as CI target

- test run again
- notebooks not yet

- notebooks are considered in coverage analysis now
   -> custom notebook runner plugin adapted
- added images for documentation

-> one place to switch between cpu and gpu

- step class for LB phasefield generic enough to work with 3-phase and
  N-phase models
- cahn hilliard can either be solved by LBM or by finite differences
- 3 phase model can be solved with rho phase or without

- 3 phase model works now with step sytem