Also merge spanners when calling stream.Score.partsToVoices

[guang-yng]

What does this PR do?

When calling stream.Score.partsToVoices, only notesAndRests are merged into the new part. We can also merge the spanners from those parts into the new one.

[coveralls]

coverage: 92.996% (+0.004%) from 92.992%
when pulling b32f683 on guang-yng:master
into f2e09f1 on cuthbertLab:master.

[mscuthbert]

Hi guang-yng -- thanks for the contribution -- I'm looking forward to being able to merge this. Make sure that spanner is not used as a variable since it overshadows the name of the module (sp is what I usually use); use an editor that follows .editorconfig formats so you don't break music21 format; and most importantly please add tests to show that the spanners are collected.

What about spanners within the part's measures? Should we be collecting them? In which case

for sp in p[spanner.Spanner]:

might be the better loop variable.

[guang-yng]

Hi @mscuthbert , thanks for the quick review! I’ll make the fixes and add test cases. Also, do you think we should merge Dynamic elements in the measures as well? Currently, only Note, Chord, and Rest are being merged. I’d be happy to include that too. Thanks again!

[mscuthbert]

For now, one PR = one feature. We can do dynamics after you have a successful merge etc.

[guang-yng]

Hi @mscuthbert, just checking in—would it be okay to merge this PR now?

[mscuthbert]

Thanks for the bump!