This changes parseDescription to properly encode things to be safe for
usage without removing things like backslashes that may be relevant.
* text.SanitizePlaintext already calls html.UnescapeString so we don't
have to do that
* Replace \n with space early
* Remove duplicate white-space by splitting on fields and joining
* HTML-escape the string we have
* For extra certainty, encode the backslash as \
Fixes#1549
