[2.0] Checklist

[brettsmason]

This will be an ongoing list of 2.0 changes as and when I think of them.

• Remove hybrid_attr system and replace with JSON-P?
• Check Gulp build system is working correctly
• Social media customizer control (sortable?) to replace menu system
• Move to flexbox
• Finish integrating new Sass structure
• Decide on a menu system and implement it!
• Clean up Sass as much as possible and make less opinionated
• Add cache busting to stop caching issues of old stylesheets
• Add additional custom customizer controls (sortable text inputs, gallery etc?)