WIP-MEI: Test for sectionFromElement()

It's very simple, but so is that function.
WIP-MEI: Unit test for scoreFromElement()

We still need an integration test, and sectionScoreCore() is still untested. At
least this is a start!
WIP-MEI: Some updates for sectionScoreCore()

Mostly in documentation, but also removing a few misleading comments, and
changing the optional parameters to a "kwargs" magic parameter.