Add vagrant support

As an exercise in Vagrant, I added a Vagrantfile and provisioning script. They'll set up an environment necessary to locally serve a Jekyll page using the same settings as Github Pages. After typing 'vagrant up' and waiting patiently for ~30 minutes, you should be able to browse to http://127.0.0.1:4567/ and see the site. I think we can improve on this first attempt by using a box that already has some of the tools installed. Still, take a look and bring it in if you think it could be useful.
We probably shouldn't start the Jekyll server from within the provisioning process. The machine isn't technically up until provisioning is finished, and Vagrant likely has cleanup work to do after provisioning.