Some of this comes from the research and tests I've done in feed2exec.

This was surprisingly hard, but I think I got it about right. The
actions do get fired twice, however, which is not great. In
particular, this will be slow on large config files.

It might be possible to avoid parsing the config file twice by
disabling the config action somehow when it's first parsed, but that
seems like a needless optimization for now.

This should actually fix undertime#19

With this, it's possible to check if a flag is set, e.g. do:

    if args.verbose:
        pass

Before this, the parameter was always set to None. Now it's set to the
`const` set by the caller or whatever value is passed as an
argument (e.g. for a --loglevel FOO argument).

It's unclear where those errors come from:

E   _pytest.pathlib.ImportPathMismatchError: ('ecdysis._version', '/home/anarcat/src/ecdysis/.tox/py/lib/python3.7/site-packages/ecdysis/_version.py', PosixPath('/home/anarcat/src/ecdysis/ecdysis/_version.py'))

They do not occur in feed2exec or other projects I have, and were not
happening before the "matrix" switch. It might be a relative import
thing, but I don't have time to diagnose this so for now just use the
workaround found here:

https://stackoverflow.com/questions/44067609/getting-error-importmismatcherror-while-running-py-test

The rationale behind this is that we want minimal entrypoints, and
they way to do that is to tell pip and other deployment tools that we
want the "wheel" dist, which is more clever about that.

I am not sure yet how this relates to setup.py.

fix a typo in CONTRIBUTING.rst

See merge request !1

The previous configuration showed usage like this:

    stressant [--disk] ...

Which seems to imply that, by default, no disk job is run. But the
usage actually said:

    --disk, --no-disk     run disk tests (default: True)

which is actually correct, but ambiguous.

Now instead, we show this in the short usage:

    stressant [--no-disk] ...

And this in the long version:

      --no-disk, --disk     run disk tests (default: True)

Which is much clearer.

Actual commandline parsing is not affected, only usage output.