Patch Automatic cleaning of HTML + Rails 3.1 asset path update

I have patched Sanitize support into markdownizer to automatically strip existing html when `markdownizer!` is called. It however still leaves the initial HTML in the original `attribute` field, however as long as this is shown without html_safe then this should not cause any issues.

I have also Updated the path the generator installs the stylesheet into to reflect the asset location in Rails 3.1 as they have moved from `public/stylesheets` into `app/assets/stylesheets`