Demonstrate support for integer values in sample exam answers

[Witiko]

This PR demonstrates the changes from istqborg/istqb_product_base#33 on the example Sample Exam Questions document:

questions:
  1:
    learning-objective: 1.1.1
    k-level: K1
    number-of-points: 1
    question: Which of the following statements describe a valid test objective?
    answers:
      a: 1
      b: 2
      c: 3
      d: 4
    correct: c
    explanation: |
      a) Is not correct. It is impossible to prove that there are no defects anymore in the system under test.
         See testing principle 1
      b) Is not correct. See testing principle 7
      c) Is correct. Testing finds defects and failures which reduces the level of risk and at the same time
         gives more confidence in the quality level of the test object
      d) Is not correct. It is impossible to test all combinations of inputs (see testing principle 2)

This PR should not be merged. Instead, this PR should be closed after istqborg/istqb_product_base#33 has been merged.

[danopolan]

This is great.