Add github method to Cheffile (similar to Berkshelf's github shortcut)

Cheffile.rb

# vi: set ft=ruby :

def github(user, repo, protocol = :git)
  prefix = {
    :git   => 'git://github.com/',
    :ssh   => 'git@github.com:',
    :https => 'https://github.com/'
  }[protocol]
  "#{prefix}#{user}/#{repo}.git"
end

cookbook 'apt',         :git => github('opscode-cookbooks', 'apt')
cookbook 'rbenv',       :git => github('fnichol', 'chef-rbenv')
cookbook 'ruby_build',  :git => github('fnichol', 'chef-ruby_build')
cookbook 'ruby',        :git => github('Bigpoint', 'ruby', protocol = :ssh)