Fixes from a first, partial pass over the kernel_callables MR

doc/index.rst

doc/ref_call.rst

doc/ref_kernel.rst

examples/python/call-external.py

loopy/__init__.py

loopy/auto_test.py

loopy/check.py

loopy/codegen/__init__.py

loopy/codegen/control.py

loopy/frontend/fortran/translator.py

loopy/isl_helpers.py

loopy/kernel/__init__.py

loopy/kernel/creation.py

loopy/kernel/data.py

loopy/kernel/function_interface.py

loopy/kernel/instruction.py

loopy/kernel/tools.py

loopy/preprocess.py

loopy/schedule/__init__.py

loopy/schedule/device_mapping.py