Activates the -w option. Turns out we still have to fix
`get_wordlist_path` at it assumes that wordlists all end in
``.txt`` (which is not true).

We expect more wordlist-specific changes, regarding signatures etc.

There is no need for us to enforce lowercase wordlist names. It
could even confuse people.

We will certainly provide other english lists as well. Therefore
we need something for distinction.

Also this method now handles names instead of language codes.

We will drop the assumption that wordlists are generally organized
by language. There are, for instance, many different language
lists available in english for many different purposes.

Therefore we will support different names for different wordlists,
but the names do not neccessary depend on a language (only).

The new option is not active yet.

The sources can be registered (as entry_points) in some arbitrary
module available at runtime. We register some modules ourselves,
'system' for starters.

Yet we do not make use of the registered sources in main(). This
will be the next step.

We now use an `argparser` options instance for get_passphrase
instead of a bunch of single args. This makes the main function
`get_passphrase` less readable (you do not see immediately what
options are really expected), but avoids misleading defaults. We
now use the defaults set in argparser options, i.e. from
`handle_options()` as single source of defaults.

Move wordlists into the new package. This should fix
the data_files problem on most platforms and in most
environments.

Seems to be really tricky to install data files in a
foreseeable location.

The more finegrained solution of conorsch might be
slightly less stable in the long run, therefore we
selected the 'package', actually.

We now read from already opened file descriptors (in get_wordlist()) only.