boundary conditions can specify how the index list should be built:
- list coordinates of domain or boundary cells (previous always inner)
- list all links or only the first link

- boundaries with same name have not been displayed correctly

- removed warnings
- added flake8 as CI target

- 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

- 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

- plotting
- calculation of force on boundary
- vtk outpu

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

- single function to create kernel for specified target
- data type creation from string - reuse numpy functionality
- bugfixes in dot display

- added functions to compute force on boundary for generic boundary and
  NoSlip
- simple calculations for serial scenarios
- to distinguish between different obstacles, NoSlip boundaries can now
  be named

- renaming because of clashes with types.py from other packages

- boundary conditions can now define their own state
- boundary classes instead of functions
- no boundary name any more
  (instead the identity is defined via instances)
- updated tutorials accordingly
- boundary handling now gets pdf numpy array instead of pystencils field

previously the value was taken from the cell next to the boundary cell (i.e. the inner cell)

- getShearRelaxationRate is a free function now -> works also with cumulant methods
- better error message when calling kernels with wrong or too few parameters
- entropic & incompressible is not working by default due to pdf shift -> added NotImplemented exception
- new creation function for 'raw_mrt' where all relaxation rates can be independently specified
- enhanced entropic creation funtion, supports omega output field now