Add testing to Rakefile
Add autotest support

Test files end with _test and are Ruby files
Test helper files end with test_helper and are Ruby files
Add simplecov support

Use simplecov for test coverage reporting.
Ensure simplecov does not run whn autotest is used.
Add tests for all code

Add tests for the greetings.
Remove code previously used to test when running directly.
Simplecov shows code is 100% covered by tests.