Improve test coverage
Implement %newimage -raise correctly

Turns out mgp doesn't support -raise!  I'm amaze.
Add synthetic tests to explore mgp's behavior
Increase test coverage: test filtering
Test overage: Presentation.load(filename)
Increase test coverage
100% test coverage, for reals

Note that the synthetic test I added while trying to reproduce this case
doesn't actually match what mgp2pdf does :/