renamed wordlist to 'securedrop'

also updated README

Fixes #16

Signed wordlist

Thank you!

"Diceware 8192 list" is not a valid reference any more.

More memorizable wordlist

We have no code-internal bugfixes, but there were erraneous
examples in documentation. We do not want to see that as official
docs in public. The new release should provide updated docs.

This wordlist was renamed to `en`. It is the default wordlist.

Give config file docs an own page.

Remove heading of configuration file section of README. It was more confusing than helpful, I think.

If we talk about configuration _files_, then tell it.

Fixes suggested by `check-manifest`. It might be helpful to deliver
also docs and tests with releases, although they are not needed to run
the software.

Normally, it would be more concise to use the more declarative name.
"en_8k" tells, how many terms we find in this wordlist. But as the
wordlist names are used in the CLI and users will normally simply
look for a wordlist in their language, it can help to keep the name
of the "default" list for each language short.

We pick the 8K lists for "default" (and not the "original" 6^5
lists), because we assume that normally people will use diceware
without dice. Also most other sources of randomness will most
probably work on a 2^x basis rather than in 6^x (and therefore
have better use for 8k lists over other ones).

Make sure that config file values are really considered by
handle_options().

We pin py.test to version < 2.8.0 to make it work with the
`--doctest-modules` option enabled. We still wait for this bug
in py.test being fixed (announced in issue tracker for 2.8.3
release of py.test).

Give hints, how to customize configuration.

As we have new features in the upcoming release, we have to bump the
minor release number, not only the bugfix number.

We do support configuration files from now on.

As we introduced an py.test autouse fixture, we cannot currently also
run doctest-modules due to a bug in py.test (2.8.1, 2.8.2):

   https://github.com/pytest-dev/pytest/issues/1057

Looks like a fix is planned for 2.8.3 release. Until then we have to
disable doctests in modules.