VirtualBox Updates

Updated to Version 3.6.0

- Moved `virtualbox-guest-addition` from `extras` to `virtualbox`
- Added `Linux` instructions to `virtualbox-autostart`

Install Script/Makefile Updates!

Big updates to the installation script, the Makefile, and added a new page to the docs.

Updated Versioning to 2.6.0

Updating Versioning to 2.6.0 (#17)