Bulk check feature enabled/disabled

[joshmfrankel]

Similiar to #22 and #30, this feature would allow for bulk checking of enabled features. Something along the lines of:

AccessControl::Features::SomePolicy.new(current_user)
  .enabled?(:feature_one, :feature_two)
  .disabled?(:feature_three)

I added a bit of chaining above to illustrate a potential compound conditional checking for two feature to be enabled while another is disabled. These could also be split out to just check enabled? or disabled? on single lines. Naming could possibly be improved as well