Make exceptions useful from the command line

I frequently use curl when testing my apps, but when better_errors intercepts an exception on those requests I get a large output that is unusable at the command line. I simply added an HTML comment to the end of the HTML that includes the exception and backtrace.

This shouldn't effect viewing the page in the browser at all, but makes life at the command line much easier when tracking down errors.

Example output, trimmed for brevity: [https://gist.github.com/4347455](https://gist.github.com/4347455)