WIP-MEI: Add integration test for scoreFromElement()

The "assert" stage is lengthy and cumbersome, but it's a good test that the
module overall is actually working.
WIP-MEI: Change parameters for sectionScoreCore()

This function will never be called without the "slurBundle" parameter, so I made
it a required positional argument. Maybe this is clearer now...
WIP-MEI: Tests for sectionScoreCore()---Part 1

This duo of unit and integration test is for when sectionScoreCore() would be
called with a <score> to process.