Bring in latest from middleman-zurb template

-- Update to ZURB Foundation 4
-- Upgrade middleman gems
-- Remove instapaper and pocket
-- Directly expose share links instead of hiding in dropdown
-- Point to CDN of fontawesome
-- Remove fancybox
-- Remove html5 shiv
-- Remove respond.js
-- Remove imgsizer
-- Upgrade jquery to 1.10.1
-- Require IE9 or above (as required by ZURB 4)
-- Lots of little changes