doc: add Sphinx skeleton
ignore Sphinx output directory
doc: document top-level commands

This is just a rudimentary way to document the top-level zpm commands.
We'll use a better tool that understands argparse in the future.
commands: add stub docstring to deploy
doc: use more light-weight haiku Sphinx theme

We should eventually customize this further to better match the
zerovm.org.
Merge pull request #34 from mgeisler/sphinx