Add an initial sketch of libpassacre.
Port passacre to use libpassacre.
Fix up how passacre is built.

This includes:
- Running cmake/make from setup.py to build libpassacre.
- Removing vcversioner, and using setup_requires instead.
- Doing some semi-complicated magic between setup.py and _libpassacre.py
  so that cffi extensions are only built during the build step and not
  just when importing the stupid thing.
- Using tox for testing.
Get travis and tox to play nicely.

Also remove .travis.install.
Use -fPIC when building libpassacre statically.
Update travis's cmake.
Don't install ykpers-cffi just for tests.
Show why tests were skipped in travis.
Automatically reverse skein PRNG output.

This makes the libpassacre API friendlier; it doesn't require the user
to know whether the bytes squeezed need to be reversed.
Fix a broken test: test_invalid_prng_method
Don't use unicode_literals in tests.

Some of the tests use strings which should be native strings: str on
python2 and python3, and it's not possible to (easily) have native
string literals with unicode_literals on.

Additionally this means I can get rid of the stupid compatibility hack I
added to _libpassacre to get tests passing on python 2.
Yaaay we support python 3.4.
License banners!
Add libpassacre things to COPYING.
Merge branch 'master' into libpassacre

Conflicts:
	.travis.install
	.travis.yml
	passacre/agent/pencrypt.py
	passacre/agent/test/test_pencrypt.py
	setup.py
Merge branch 'libpassacre'