Update Invoke Tasks and use Twine for upload

Update Invoke Tasks and use Twine for upload

None of the tasks generated by the boilerplate included the 'context'
argument required by the newest version of invoke.

The 'invoke publish' task has been updated to use 'twine upload' instead
of the less-secure 'python setup.py register/upload', and comments have
been added to clarify possible steps needed to publish anteater.

A 'invoke build' command has been added to build a source distribution
and binary wheel distribution.

JIRA: RELENG-237

Change-Id: I9ae705332b592ef8880d52b7d20624180e23677a
Signed-off-by: Trevor Bramwell <tbramwell@linuxfoundation.org>