Generalizing to convert any HTML (incl. email!) to markdown

When "strip_tags" option is on, divs vanish. However, they often need a line feed.

I chose to add a paragraph break, but a line break would be just as ok for me.

Thanks for the great code!
It would be better to handle the !$diveIn case first and return early. Less diff churn and easier to examine these lines when doing a git blame.