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

- small (length < 5) arrays with shape and stride information had to be
  memcpy'd to the GPU before every kernel call
- instead of passing the information as arrays, the single elements are
  passed
- leads to more function arguments, but simplifies GPU kernel calls

-> changes in all backends required

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

- fix for field collection and reduction operations
- support for aligned fields in parallel data handling

- 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

- update kida vortex benchmark

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

- works also with ps.kernel decorator

- 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

- plotting
- calculation of force on boundary
- vtk outpu