Added TODO tests to test framework.

* Added functions 'TODO' and 'END_TODO'.

* Added documenting comments.
Named test framework 'Dashtap'.

* Separated the TODOs of the main project (Fix.sh) and the test
  framework (Dashtap) into separate files.

* Renamed 'test-functions.sh' -> 'dashtap.sh' and modified all
  invocations thereof to use the new name.
Added document comments about shell unit testing.