Rename s3file class to s3::file

I could not get 's3file' to work on Puppet 2.7.11.  Comparing this definition to similar objects I used elsewhere, I found that qualifying the name of the module and the name of the defined object worked well.  I renamed the module  from s3file to s3, and renamed init.pp to file.pp, so the define formerly known as s3file is now known as s3::file.

My assumption here is that the 's3file' construct no longer works in Puppet 2.7.x, and that you must have created this definition on an earlier version of Puppet, where placing a define in an init.pp file was okay.  I don't have a ton of experience with Puppet, though, so feel free to tell me I'm off base here.  The main reason I am submitting this as a PR is that my PR on your minecraft module depends on this change.