git ssb

Improve logic (again) for stripping the post title out of the body

If the first line is short enough to be the title,
and the second line is whitespace-only,
then strip the first 2 lines from the body.
Otherwise, the body is always the entire text.

This should prevent splitting a paragraph,
quote, list or similar block.

This still doesn't handle a markdown list of paragraphs,
where each item is separated by a blank line.

It also doesn't handle Setext-style headings
(underlined with '====' or '----').