usfm2osis.py - processing the speaker tag \sp_text

In the USFM Reference, the speaker tag \sp_text is listed under Titles, Headings, and Labels.

Speaker Identification (e.g. Job and Song of Songs)

This implies that when converted to the OSIS speaker element, it should not be part of poetry lines or list items.
Rather it should be treated like a title element.

Furthermore, the element <speaker> is not allowed within the line group element <lg> yet it is allowed within the line element <l>, even though as a title, it makes no sense in that context.

For this reason, processing the \sp_text marker should force the closure of poetry lines and the line group.

It should also force the closure of list items and the list element.

Unlikely as this may be, it should force closure of any table element too!

Implementing this correction will result in valid OSIS, all other causes of validation failure being absent.

Not implementing this leaves the high likelihood of generating invalid OSIS.