Merge branch 'InterpolationBC' into 'master'

doc/img/Boundary.pdf

doc/img/Boundary.svg

doc/notebooks/00_tutorial_lbmpy_walberla_overview.ipynb

doc/notebooks/04_tutorial_cumulant_LBM.ipynb

doc/notebooks/demo_interpolation_boundary_conditions.ipynb

doc/notebooks/demo_shallow_water_lbm.ipynb

doc/sphinx/lbmpy.bib

doc/sphinx/tutorials.rst

lbmpy/__init__.py

lbmpy/advanced_streaming/__init__.py

lbmpy/advanced_streaming/indexing.py

lbmpy/boundaries/__init__.py

lbmpy/boundaries/boundaries_in_kernel.py

lbmpy/boundaries/boundaryconditions.py

lbmpy/boundaries/boundaryhandling.py

lbmpy/custom_code_nodes.py

lbmpy/maxwellian_equilibrium.py

lbmpy/sparse/mapping.py