update documentation of type system

docs/source/api/index.rst

docs/source/api/types.rst

docs/source/api/types/basic_types.rst

docs/source/api/types/quick.rst

src/pystencils/backend/kernelcreation/typification.py

src/pystencils/types/__init__.py

src/pystencils/types/basic_types.py

src/pystencils/types/quick.py