Add Gemfile with test dependencies
Add initial ChefSpec tests
Add custom matcher for homebrew_cask LWRP

Since homebrew uses package, we can use the built in ChefSpec
install_package. However, homebrew cask packages use the homebrew_cask
LWRP, so we have to create a custom matcher.
Add test for one of the homebrew cask packages
Run tests against all defined packages.
Don't auto update because duplicate git resource
Make RSpec run default Rake task
Add Travis support