- started with generalized free energy formulation

- removed warnings from generated code
- made generated code string deterministic, generating the same twice
  gives binary equally files now

- 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

- Equilibrium class did not do "+1" density shift correctly
- support for generating single precision models

- separate lbmpy module
- code generation for walberla
- isolated code to generate a listlbm update rule from collision rule

- test run again
- notebooks not yet

- 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

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

- 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

- 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

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

- added rudimentary test to prevent these kind of problems