Add new S3 library and make the plugin work again!

When I first tried to use this plugin it didn't work - I kept getting errors uploading to S3.  It seems the API has changed since the plugin was first written.

The original code for the S3 library is hard to follow so I didn't spend a ton of time on it.  Instead, I included a simple library from https://github.com/tpyo/amazon-s3-php-class and hooked that into the 'put object' function.  

This is far from an elegant solution and I'm sure it could be improved a lot.  But if you just want the plugin to work again, this PR will restore a basic level of functionality.