short display of test run results using options.display

When running a very long list of specs, the console output can become unusable (e.g. 1500 tests). To that effect, it would be nice to just get green checkmarks when a test passes, and a red x for failling tests.

This pull requests allows this by providing a 'display' options that takes 'full' (the current and default behavior) and 'short' (the version added in this pull request)

Documentation was updated, tests are green!