add variables for heading font sizes; fixes #9921
regenerate customizer's raw-files.js
add header font size vars to customizer page
Merge branch 'master' into header-font-size-vars
Update and document use of `small` in headings
Run grunt dist on theme for some reason
run grunt
Merge pull request #9966 from twbs/header-font-size-vars

add variables for heading font sizes; fixes #9921