Add white-space: pre-wrap to the default CSS.

Make preformatted text wrap by default, so that you don't have to scroll
countless furlongs horizontally or copy and paste into a local text
editor in order to read long log output.

Pre-wrap appears to be supported in all modern browsers. "word-wrap:
break-word" could be added if support for IE <= 7 is desired.
Add a note about default.css wrapping preformatted text.
Merge pull request #599 from geraldcombs/master

Make preformatted text wrap by default