Changed README, filenames, and gem's structure

I was getting an exception when trying to start the server. It turned out to be a bug in the way the view helper was being loaded, so I changed it over to a more standard approach.

Summary:
* Made README useful.
* Used Railties to include the view helper to fix server startup exception.
* Renamed initializer assets to predictable names.
* Make the scoping (Pdfjs::Rails) consistent across all the files, including the helper

Thanks !!