Merge branch 'fhennig/loop-invariants' into 'backend-rework'

docs/source/backend/index.rst

docs/source/backend/translation.rst

src/pystencils/backend/ast/analysis.py

src/pystencils/backend/ast/expressions.py

src/pystencils/backend/ast/structural.py

src/pystencils/backend/constants.py

src/pystencils/backend/emission.py

src/pystencils/backend/kernelcreation/__init__.py

src/pystencils/backend/kernelcreation/ast_factory.py

src/pystencils/backend/kernelcreation/context.py

src/pystencils/backend/kernelcreation/cpu_optimization.py

src/pystencils/backend/kernelcreation/freeze.py

src/pystencils/backend/kernelcreation/iteration_space.py

src/pystencils/backend/kernelcreation/typification.py

src/pystencils/backend/platforms/generic_cpu.py

src/pystencils/backend/platforms/generic_gpu.py

src/pystencils/backend/transformations/__init__.py

...ystencils/backend/transformations/canonicalize_symbols.py

...pystencils/backend/transformations/eliminate_constants.py

...ils/backend/transformations/hoist_loop_invariant_decls.py