- test run again
- notebooks not yet

- assignment collection
- sympyextensions

- added documentation
- PEP8 renaming

- Previously sympy.Eq was used to represent assignments. However Eq
  represents equality not assignment. This means that sometimes sympy
  "simplified" an equation like a = a  to True,
-> replaced sp.Eq by pystencils.Assignment everywhere
- renamed EquationCollection to AssignmentCollection

- switched to google style docstrings
- removed dead code
- started to annotate types

for fields without index dimensions the indices (0,) and () have been
treated equivalently, but did not compare equal

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

- shortened the longest running tests, moved some configurations
  to longrun

Modified the gitlab-ci for benchmarking purposes
Created a new Dockerfile for benchmarking purposes, which includes the
intel compiler.
Docker file now has likwid installed as well.
Created a machine file for the benchmarking machine.
Kerncraft updated and fixed.

TODOs:
    - cleanup of the yaml files
    - Test the Skylake machine file and kerncraft_coupling for correct
      behaviour

-> one place to switch between cpu and gpu

label -> target
ceIdx -> superscript

- merged finite difference functions into one function
- put derivative operators from lbmpy into pystencils

- in-kernel Neumann boundaries
- flag-interface for boundary handling makes one flag field multiple
  boundary handlings possible
- generator: support for bitwise logical operators

- splitted existing LBM boundary handling into two parts:
    -> generic part , that is used for FD as well and moved it to pystencils
    -> LBM specific part - remained in lbmpy

- bugfixes

- 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

- now an lbMethod or updateRule can be passed in directly
- made method/update rule/ast function independent i.e. no function
  uses the same parameters as on of the others

- 3 phase model works now with step sytem

- plotting
- calculation of force on boundary
- vtk outpu

- previously all objects where cached by id()
- for waLBerla simulations in each time step a new np.array view
  is created from the waLBerla field. Each of these views has a
  different id -> caching did not work for waLBerla setups
- changed hash for numpy arrays: instead of id, a tuple of
  (dataPtr, strides, shapes) is used as hash input

- Step working for serial CPU scenarios

- scaling interface width eta instead of surface tensions tau to correct
  interface profile & surface tensions