Merge branch 'rangersbach/reductions' of i10git.cs.fau.de:pycodegen/pystencils into rangersbach/reductions

# Conflicts:
#	src/pystencils/backend/platforms/generic_gpu.py

# Conflicts:
#	src/pystencils/backend/platforms/cuda.py
#	src/pystencils/jit/gpu_cupy.py

HIP Target and Platform

See merge request !458

Optimization for GPU block size determination

See merge request !454

# Conflicts:
#	src/pystencils/codegen/driver.py
#	src/pystencils/include/pystencils_runtime/hip.h

Fix Linear3D Indexing if Iteration Space Rank < 3

See merge request !457

Some cleanup to the pystencils runtime headers

See merge request !456

Introduction of structural ast nodes

See merge request !455