Enhanced volume breaking

[bertfrees]

• It must be possible to ensure that text elements (paragraphs, list items, anything) do not cross volume boundaries.
• It would be nice to have the option of inserting manual volume breaks.
• It would be nice to have "intelligent" flexible breaking (favouring volume breaks at headings, for example), but this is the least important issue for us in this regard.

+1 from:

• NLB: Automatic volume breaking nlbdev/pipeline-mod-nlb#58
• SBS: Make manual volume breaking work properly sbsdev/pipeline-mod-sbs#33 (manual volume breaking)
• Dedicon: Enhanced volume breaking pipeline-mod-dedicon#53

[bertfrees]

A part of it is already supported, and just needs to be tested (notably manual breaks and intelligent breaks). Another part (notably not splitting text elements) is not supported yet.

See daisy/pipeline-mod-braille#136.