Add the build configuration and integrated test to generate a
Python distribution package named `tflite_micro` for publishing
the tflm interpreter as a Python module with a native extension.

Use the build tools provided in @rules_python, augmented by a
custom rule `py_namespace` for the reasons documented in
`python/py_namespace.bzl`.

Provide an integration test at `//python/tflite_micro:whl_test`.
Use a .tflite model copied from the hello_world example. (Copied
to avoid creating a dependency.)

BUG=part of tensorflow#1484