Add unit tests everywhere

[dascandy]

No description provided.

[dascandy]

Note to this effect in DESIGN.md.

[dascandy]

Target percentage for this issue is 50% as measured and reported by coveralls (or some other online service), and tested on both Appveyor and Travis.

[PenguinLemma]

Hi, I would be happy to help by adding some more unit tests, if that's fine for you.

Also, in the case in-code documentation is wanted (e.g. // Method A checks this and outputs that, using doxygen and the likes) it would make sense to do it along the way, since writing tests will require understanding the intent of the units. Documentation could be included in a separate issue.

Let me know what you think! :)

[dascandy]

We need some form of documentation, but I have no huge preference for the format. If you think using doxygen comments will generate good documentation, please go right ahead!