Remove the trailing blank line in markdown text.
The markup() function returns a string with an extra blank line (as

every HTML tag is outputted with a trailing newline). We don't really

want this, since it leaves a blank line in each <pre>, so check if

there's a newline and strip it away. This brings the look to how we had

things pre-markdown.

Tested locally with different text. The textboxes no longer had the

annoying final newline.
Unit tests pass.