Add unit tests to the problems in this repository.

[iduhetonas]

Other considerations:

• Generic enough to run without too much intervention (i.e. don't update unit-tests whenever a new function is created).
• Has a build-tools directory for automatic running. Subset of the first point.

[iduhetonas]

First step finished, as (almost) all directories can be imported as module libraries. Using http://book.realworldhaskell.org/read/testing-and-quality-assurance.html as a guide for unit tests.