Clean up library dependencies and documentation

* Upgrade Ruby patch level to 247.
* Wrap documentation lines at 80 characters.
* End sentences with periods.
* Replace Bourne with RSpec Mocks >= 2.14, which now has stubbing and
  spying.
* Upgrade Rake.
* Use RSpec `expect` syntax.
* Configure RSpec to fail fast, saving time during TDD loops and
  CI runs.
* Configure RSpec to run tests in random order, potentially exposing
  inter-dependent tests.