WIP-MEI: Tests: New tests for _barlineFromAttr()
WIP-MEI: Tests: New tests for _tieFromAttr()
WIP-MEI: Tests: New tests for removeOctothorpe()
WIP-MEI: Tests: New test for articFromElement()
WIP-MEI: Tests: New test for accidentalFromElement()
WIP-MEI: New: Experimental strategy for properly setting <mRest/> durations

I'm hiding this in measureFromElement(), which is the earliest point at which
the importer knows the full expected duration of a measure. This also happens
to fill "empty space" in a situation where not all events were imported.