Works with latest version of Devise and is customizable

I had modified this originally and released it as my own gem because I wasn't quite sure how this works.  I took the original gem and modified it to take a time argument for checking if a user is online, on the website I use it on 15 seconds makes the most sense because it is a social network and uses Ajax, so if the browser is open it is registering activity constantly.

It also works with the latest version of Devise in the latest Rails, which was my original reason for modifying it, it wasn't working for me.  Anyhow it'd be cool if you want to merge it back in.  We can change the names back to onliner instead of onlinerbytodd if you want.