zpm,commands: create_project returns zar.json path

The `zpm.create_project` function now return the full zar.json path,
which allows the command line interface to notify the user that the file
was created. We now print the full path, instead of just telling the
user into which directory the file was created. I think this is more
useful and explicit.
test_zpm: update test with _create_zar_json retval

Since this function now returns a value, this change updates the test to
check the return value.
Merge pull request #62 from larsbutler/fix-zpm-new-2

Fix `zpm new` command, part 2
doc: use new zerovm Sphinx theme

This is a rough adaptation of the "nature" theme for Sphinx with the
colors used on zerovm.org. Things like fonts, text sizes, paddings and
margins are still missing.

I'll most likely repackage this later as a stand-alone Python project
so we can reuse it in other contexts.
tox: include {posargs} in sphinx-build cmdline

This is very useful for testing the documentation: you can run

  $ tox -e doc -- -E

to completely rebuild the documentation (the -E flag makes
sphinx-build ignore the cached environment).
Merge pull request #64 from mgeisler/zerovm-sphinx-theme

Add a ZeroVM Sphinx theme for docs
Move `deploy` code to zpm module

This minimizes the amount of code in the `deploy` command wrapper
function, and moves all of the logic to an API function in the `zpm`
module called `deploy_project`.

TODO: Break up the `deploy_project` into smaller chunks and write tests
for it.