Also update style.css to hide outline of editable text areas and apply
correct styles to line numbers in non-playground snippets.
R=golang-dev, r
CC=golang-dev
https://golang.org/cl/13946043
Remove References section heading.
Add redirects from old paths to new content.
Add a link to the SubRepositories wiki page from package list.
Add styles for "pop-out" link.
R=r
CC=golang-dev
https://golang.org/cl/13356047