Adding passacre.generator.SpongeRandom.

This is useful for more complicated repeatable-pseudorandom generation using
the Keccak sponge as an entropy source.
Add ~/.config/passacre/passacre.yaml.
Add clipboard support via xerox.
Add clipboard timeout.
Refactor for flexibility of generation options.
Refactor to using the random.Random interface.

This allows other seeded PRNGs to be swapped in instead of Keccak.
Doing more refactoring; updating an explanation.
Allow arbitrary config options.
Start on python 3 compatibility.
Continuing python 3 compatibility.
Still more python 3 compatibility.
Oh no! More python 3 compatibility!
Yet more python 3 compatibility.
Add skein; remove compatibility mode.

For some reason, the random module wasn't too happy with Skein's
Random when using randrange with a really big number.
Refactor more; make cykeccak and pyskein optional.
Merge branch 'sponge-random'

Conflicts:
	passacre/application.py
	setup.py
Improve UX a bit.

Silence KeyboardInterrupt errors from interrupting the password timeout; notify
the user when the password has been copied.