Move the bulk of the raygun logic out of the bin and into the lib.
Download the app protoype from github instead of embedding it.

- Fetch the latest tag from carbonfive/raygun-rails4.
- Check to see if the tarball is already cached under ~/.raygun.
- Download if it's not cached.
- WIP: Check that the raygun gem is new enough for the protoype.
- Generate the new app using the newest tarball.