Update 1520ify filter

[benory]

This updates the 1520ify filter with the remaining cleanup needed for 1520s Project conversion output.

Main changes:

• handles mensuration labels from text and converts them into the appropriate *met(...) interpretations
• supports additional default mensuration-to-*met(...) mappings, including *M6/2 and *M9/2
• incorporates barnum -a-style numbering for ordinary barlines, leaving final barlines unchanged
• improves terminal long handling, including internal section boundaries
• computes !!!voices: from active voices by section, allowing ranges such as 2-4 when sections differ
• normalizes !!!!SEGMENT: filenames to .krn
• splits encoder/date information from !!!ENC: into !!!ENC: and !!!END: where applicable
• adds !!muse2ps: spacing defaults when absent
• updates the generated min/humlib.* files to match the source/header changes

[benory]

After this is reviewed, I can open a separate PR for the jrpize filter which has many of the same features.

[craigsapp]

computes !!!voices: from active voices by section, allowing ranges such as 2-4 when sections differ

This is interesting. Perhaps call it !!voices: as a global comment? I treat three !!! as "timeless" (applied to the entire file, and two !! as "timed", having a specific time point.

[benory]

I see the distinction you’re making. I’d prefer to keep it as !!!voices: because this is meant as a file-level summary, not a timepoint annotation.

For The 1520s Project files we’ve prepared so far, this has been the convention: !!!voices: records the overall voice count for the file. When the number of active voices changes by section, I’ve been writing that as a range such as 2-4. The change in this PR just automates that existing cleanup step so I don’t have to do it manually.

[craigsapp]

That is good: there will be complication either way...