Control output format

[dbosk]

Right now the output format is forced to be \question for the exam format. exercise environments are translated to \questions.

We'd like to do the other way around too. We might want to create slides with old questions or exercises filtered out.

Also we might want to use different environments than just exercises.

[dbosk]

Very much related to #54. Map overlap.

[dbosk]

We should support the use of

• text2qti
• qti2txt

[dbosk]

Output either LaTeX (question, exercise) or Markdown (text2qti).

Parse out the parts, then use pandoc to convert between formats.