Packer file that creates VirtualBox, VMWare and Amazon EC2 VMs from the Cypress build script

Updated gitignore to ignore Packer cache/output

Updated contrib README to include cypress.json

Added compressor post-processors for the two VM builders

Added Packer-built tarballs to gitignore

Preseed file for Packer VM bootstrapping
Merge pull request #61 from okeefm/packer_build

Packer file that creates VirtualBox, VMWare and Amazon EC2 VMs from the ...