Shan-Chen tutorial

See merge request pycodegen/lbmpy!8

implemented unconventional D3Q27 stencil by Abbas Fakhari

See merge request pycodegen/lbmpy!7

implemented the phase_field model of Abas Fakhari

See merge request pycodegen/lbmpy!6

- str(e) did work in previous pytest version
- but the correct usage is str(e.value)
- in newer pytest version the string for the e object is changed so
  the tests did not work any more

Remove obsolete fluctuatinglb.method_with_rescaled_equilibrium_values

See merge request pycodegen/lbmpy!5

Fluctuating LB needs zero mean and unit variance random numbers

See merge request pycodegen/lbmpy!4

Magic block offset symbols for Walberla

Closes #2

See merge request pycodegen/lbmpy!3

- variances from temperature
- seed parameter
- block offset parameter