Handling of single linebreaks in difftext causes people to use it wrong

[robinharms]

• They're almost never added as bulleted lists, and there's not a single meeting so far where this hasn't been missused.
• As soon as a soft linebreak is added, it causes large chunks of texts to be interpreted as a bulleted list.
• Line by line diff is almost always done by accident.

Questions to solve:

• Should we allow line by line diff at all? Is it worth the hassle?
• How should it be enabled in that case?