codex.wordpress.org/Theme_Customization_API
developer.wordpress.org/themes/advanced-topics/customizer-api
en.support.wordpress.com/customizer
wordpress.tv/2016/01/09/dave-green-building-themes-with-the-wp-customizer-api
wptavern.com/wordpress-org-now-requires-theme-authors-to-use-the-customizer-to-build-theme-options
