Add Vagrant configuration and Rake tasks for testing.

There is now a Vagrantfile in place that brings up a box appropriate for
running tests on. Tests are forthcoming.
Change default ruby to something less old and busted
Minor refactors and added tests.

* Rely on a properly configured linker path to locate the library.
* Detect availability by attempting to load libkeyutils.
* Add tests.
Break apart tests into separate files
Update README and documentation to reflect changes
Merge pull request #1 from ahorner/minor-refactors-and-tests

Minor refactors and tests