Add nox.options which allows specifying command-line configuration in the Noxfile

[theacodes]

Closes #141

@dhermes, @lukesneeringer I would appreciate a critical eye here. I'm not 100% sold on the way I did this internally.

[dhermes]

Put ... instead of pass?

[theacodes]

Done.

[dhermes]

When does this get verified?

[theacodes]

Same place as the command-line arg, during tasks.filter_manifest -> manifest.filter_by_name. It'll barf if you pass garbage, ofc.

[dhermes]

Any plans for checking if this goes stale? Something like:

.. testsetup:: foo

    import nox
    def info(attr):
        return getattr(nox.options, attr).__doc__

.. doctest:: foo

    >>> names = sorted(dir(nox.options))
    >>> for name in names:
    ...     print(name)
    ...     print('    {}'.format(info(name))
    envdir
        Equivalent to specifying ...
    sessions
        Equivalent to specifying ...
    ...

[theacodes]

I think we're going to remain relatively conservative on adding new command line args (I say this as I'm writing a PR to add a new one...). I also don't have doctest setup yet, so.

[dhermes]

I also don't have doctest setup yet, so.

That's a bad reason?

But it's up to you. That was just a suggestion. You wouldn't get pretty CSS in a doctest. Or maybe it's possible, I just don't know how.

[theacodes]

It's not a great reason to never do it, but it's a good reason not to do it right now. We can file a bug and pick it up later. (e.g. perfect being the enemy of good here, especially for collateral like documentation).

[dhermes]

Indeed. Feel free to file if you like the idea / if you want doctests. I love doctests and forbid code-block:: python in some projects (e.g. bezier)

[dhermes]

1. Why the removal of .nox as default?
2. Setting formatter_class=argparse.ArgumentDefaultsHelpFormatter will actually document your defaults so you don't need to write it in your prose

[theacodes]

Leaving .nox as default makes it impossible for me to tell if it was specified at the command line or not. Leaving it as "None" allows me to distinguish that, and the default assignment is moved into merge_from_options.

[dhermes]

LGTM