* Issue #152: Made simple-cipher more approachable by splitting test classes in a more sensible way and making clear which steps they relate to.

* Changed SimpleCipherTest to use the junit Rule annotation for expected exceptions. Changed variable names in SimpleCipherTest to be more descriptive and moved the test cipherThrowsWithEmptyKey from step three to step two.

* Added HINT.md which explains how to run only one test class.

* Changed HINT.md in simple-cipher to refer to the actual test file names and not to contain the same information as in SETUP.md