- assignment collection
- sympyextensions

- 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

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

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

- compute forces from pressure tensor instead of mu field

- collide-stream is the theoretically correct order - streamCollide
  optimization is not valid in all settings (e.g. when coupling to other
  methods)
- however, collide-stream is more expensive - since two sweeps have to be done

- systematic derivation of pressure tensor
- can be used alternatively to the chemical potential to obtain forces

- 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

- Step working for serial CPU scenarios

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