This function provides pure WordList functionality and should be
part of this class therefore.

We do not need `basestring` (or some Py3 equivalent) to check for
strings.

The functionality is replaced by the WordList class.

We do not support closing file descriptors automatically with
WordList. But (beside the fact that WordList instances require less
memory), we support reading a wordlist several times.

Make sure WordLists handle open file descriptors correctly.

WordLists should generally fullfill all promises of get_wordlist,
except closing file descriptors. The latter is not supported because
we might want to read a file several times.

We also support cryptographically signed wordlists with WordList instances.

It is better readable.

Make sure signed entries are stripped also if dash-escaped.

Create a single place where lines of wordlists can be refined,
regardless of their mode (crypt-signed or not).

We ignore empty lines also in signed wordlists. To check it, we need
an empty line in the sample.

Many wordlists have format "NNNNNN<tab>some-term". We try to
detect lines of this format and will parse them to get the term
(removing numbers and whitespaces).

and do not strip() if done already.

We need this regular expression to strip entries in wordlists like
the original 7776-terms wordlist from diceware.com.

As described in RFC 4880, dashes in wordlists might be escaped.
We have to take care of this when extracting wordlists.