assemble tool

[craigsapp]

Implement an assemble tool in humlib that knows about extended rhythms (and grace notes).

Related to issue #100 (comment)

[craigsapp]

Related to implementation of this tool, integrate with the Humdrum-to-MEI converter so that orchestral scores can be edited in VHV by part rather than score. To do this, add a segment prefix to the XML IDs in the MEI data, such as note-S4L112F2, which would mean "the second field on the 112th line of segment 4". The line number would be in reference to the exclusive interpretation line that starts the segment (there could be negative lines for reference records above this line that are in the same segment. This will greatly simplify editing orchestral scores in VHV.

A universal reference record could be used to automatically indicate that the data is encoded by parts rather than by score (so not necessarily only implemented by !!!!filter: assemble.

The parts should be ordered from highest to lowest, but there should be an option to reverse the order.