make a vagrant box to make things easier

Maybe a vagrant box will be less work for users. At the moment the
Vagrantfile is just pointing to a remote url, but in the future it
should contain the actual scripts to construct the box so that the box
can be updated as the dependencies in the repository change.
Merge pull request #261 from kanzure/use-vagrant

Downloadable virtual machine image (Vagrantfile and box)