Add validation of manually written exams

[dbosk]

Occasionally one feels the inspiration flowing and one writes a full exam manually. To aid this work it would be nice to have a validation option which simply processes the questions of an exam and checks whether all ILOs are covered.

[dbosk]

This can be solved without any extras at the moment:

examgen -NCE -d the_exam.tex -t ILO1 ... ILOn > /dev/null

If you get an error, you'll know which ILO isn't covered or should not be included. No error means you're fine. However, this statement should be proved.

A slightly more relaxed version, ensures you haven't forgotten anything, is:

examgen -C -d the_exam.tex -t ILO1 ... ILOn > /dev/null

[dbosk]

We can add this claim and its proof to the documentation (Sect. 5 Usage examples).