Remove usage of old classmethod and the method itself.

This one is supposed to replace the existing classmethod and should become a regular fixture.

Looks like there are no problems with Python 3.6 yet. We make it a
regular target in tox and will start official support in `setup.py`
after a while.

Tell about the new default wordlist.

The EFF list is currently certainly the scientifically most advanced
list. Thanks to @anarcat for proposing this switch! The securedrop
list is still available.

Although the changes since last release are not very severe, it
is a difference to "no changes yet". Trusting the latter can make
things complicated.

Yet we only allowed expressions like '2012, 2014' etc. when telling
which year a copyright was assigned at. Now we also allow ranges like
'2012-2014'.

Thanks to @drebs for spotting this one.

We must tell, that this option does turn words into lower-case
automatically.

Fixes #32.

Fixes #31 completely. The real fix was already
applied by @LogosOfJ (by fixing my broken tests
for `RealDiceSource`).

This additional test just runs `diceware` virtually,
with `realdice` as source of randomness.

We want that kind of fake input for other tests as well and will
turn it into a pytest fixture.

Small fix for RealDiceRandomSource

RealDiceRandomSource and its tests updated to expect argparse.Namespace objects instead of dicts (fix for using the 'realdice' randomness source)

We support py3.5 but not py3.2. This was yet told incorrectly in
README.

Thanks to @lieryan for bringing the problem up.

Use pytest automatically, when `python setup.py test` is run.

We can tell `setuptools` to use `pytest_runner` when setup.py is
invoked.

Use of ``[pytest]`` section in `setup.cfg` is deprecated while
the new section name ``[tool:pytest]`` is not recognized by older
`pytest` versions.

To stay compatible with older `pytest` and avoid warnings with
`pytest` 3.0+, we move the whole config to `tox.ini`, where still
the old section name is valid.

Maybe we should switch to the new(?) file format used by Debian?