Added exception and backtrace as a comment at the bottom of the HTML

I frequently use curl testing in Rails, 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
Better Rails 3.0 comaptibility

Sice latest 3.0 Rails version (Rails 3.0.17) depends on erubis ~> 2.6.6, it is not usable with better_errors gem now.
only show better errors on localhost (closes #36)
Merge pull request #80 from simi/patch-1

Better Rails 3.0 compatibility
Fixed typo
Merge pull request #83 from picandocodigo/master

Fixed typo
Merge pull request #79 from csexton/html-comment

Make exceptions useful from the command line
Update README.md
Merge pull request #88 from auxbuss/master

Documentation update
remove display:none from backtrace frames
don't parse backtrace strings for file and line info
Naive fix to allow using Better Errors with Turbolinks. Closes #91.
Turbolinks: make the reload button work still. See #91.
Move text rendering to a separate template (text.erb). See #87.
Serve the text-only page for non-graphical browsers. See #79.
Display code in the text-only version.
Show file/line number in the text template.
Don't escape HTML in the text layout.
Rewind rack.input before reading from it
Merge pull request #94 from virusman/rewind-fix

Rewind rack.input before reading from it