Include documentation of the utility modules

Add a documentation section that uses the automodule
sphinx documentation generator to build a utility page
that shows people what the utility modules taskflow
uses for *internal* usage are and include a warning to
try to avoid end-users from using these modules (better
to warn than not warn).

This also adds on docstrings to various functions that
were missing it so that they appear correctly in the
generated documentation.

Change-Id: Ibd5695927601614f31793ea5450887694f4320ae
Merge "Include documentation of the utility modules"