We had previously defaulted to slideLevel 2. Now we use the correct
behavior of defaulting to the highest level header followed by
content. We change an expected test result to match this behavior.
This is the beginning of a test suite for the powerpoint
writer. Initial tests are for the number of slides.
Note that at the moment it does not test against corruption in
Microsoft PowerPoint; it just tests that certain outcomes work as
expected. More tests will be added.
This test framework uses the PandocPure monad introduced with Pandoc 2.0.
