Control formats for output

[dbosk]

Right now we only output in the original format of the question, i.e. an exercise as input will be an exercise in output. We must convert them to a homogenized format, so that all chosen questions are in the same format. format. We should be able to output

• \question non-environment;
• exercise;
• problem;
• question, questionmult, choice, choices

environments too.

[dbosk]

This must take #23 into consideration.