Enable takt barlines and import from Volpiano

[rettinghaus]

This PR adds reading/writing of visual attributes for barLine, enabling to draw single barlines as takt.
Also it adds basic import for barlines to Volpiano support (including breaks, which are shown as takt barlines).

Example

1---dcd---3---fef---7---dcd---4---fef---77---

[ahankinson]

I think this is missing functions for 5 and 6 too, right?

[craigsapp]

Can number 7 (takt) be used in CMN or is this specific to neume notation? Or in any case verovio allows using it with MEI-all? I came across it last week in a modernized version (from 1877 publication) that is transcribed from earlier notation:

Either it comes from the original notation, or it was added to mark phrase boundaries/verse line. It does not occur at the colon (:) which is a regular barline

[ahankinson]

It's all a bit weird, because technically these are more like breath marks / articulations than "bar lines".

[craigsapp]

Perhaps, but they are not in all examples, so probably original from the original melodies. It could be that the original notation did not have barlines, but had takt only for the phrase boundaries (breath marks).

Here is a case where the takt is use to split 6/2 measures in half, so it can't mean breath marks in this song:

paper page 541 in:
https://rosdok.uni-rostock.de/mcrviewer/recordIdentifier/rosdok_ppn738218359/iview2/phys_0643.iview2?logicalDiv=log_0016

Some German can read the Fraktur font to see if its purpose is described in the introduction:-)

[ahankinson]

I guess we should also figure out if <barLine> is appropriate, or <divLine>?

https://music-encoding.org/guidelines/dev/elements/divLine.html

https://de.wikipedia.org/wiki/Pausa_(Neume)

[rettinghaus]

@ahankinson I've added ending baronies, but short bar lines are not available yet. And from what I get from Volpiano these are all bar lines.

[ahankinson]

Well, kinda. Volpiano is designed as pseudo-chant, but with everything in modern chant it gets filtered through CMN.

Here's what the Liber Usualis has to say about these symbols:

So it may be that the creators of Volpiano thought of them to be like bar lines, but they were probably representing concepts that were closer to the diviso of the LU.

With Craig's example the takt seem to be more phrase markings than bar lines. Who knows, but we can't create a standard encoding based on a single weird source.

[ahankinson]

Preliminary tests indicate that <divLine> may work, but it needs a bit of finessing. So we can accept this PR, but the actual implementation may change later.