Refactor Field Modelling

docs/source/backend/ast.rst

docs/source/backend/index.rst

docs/source/backend/objects.rst

docs/source/backend/output.rst

src/pystencils/backend/__init__.py

src/pystencils/backend/arrays.py

src/pystencils/backend/ast/analysis.py

src/pystencils/backend/ast/expressions.py

src/pystencils/backend/ast/structural.py

src/pystencils/backend/ast/util.py

src/pystencils/backend/emission.py

src/pystencils/backend/extensions/cpp.py

src/pystencils/backend/jit/cpu_extension_module.py

src/pystencils/backend/jit/gpu_cupy.py

src/pystencils/backend/kernelcreation/ast_factory.py

src/pystencils/backend/kernelcreation/context.py

src/pystencils/backend/kernelcreation/freeze.py

src/pystencils/backend/kernelcreation/iteration_space.py

src/pystencils/backend/kernelcreation/typification.py

src/pystencils/backend/kernelfunction.py