add extend content-block
add .prose list, block-text styles
fix accidental prose class on basic footer
add %prose and %paragraph-header
add %href-on-black on footer links
fix %content-block so it doesnt interfere w/ grid mixins
add styles to work w/o .prose
remove .prose on social-media examples
add .about grid mixin, ensure <pre> full-size
apply mixin list-grid to .about