golang.org now serves HTTPS with a valid cert, so it's reasonable
that users should click through to the HTTPS versions of *.golang.org
and other known sites.
LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/112650043
Remove "References" section.
Remove most articles and redirect to blog.golang.org.
Move /ref/spec and /ref/mem to /doc/spec and /doc/mem.
Remove duplicate links from the remaining
"Documents", "The Project", and "Help" pages.
Defer to the wiki for more links and community content.
Update command reference and mention cover tool.
Add "Pop-out" text to the front page.
Pick one of four videos at random to feature on the front page.
Fixes#2547.
Fixes#5561.
Fixes#6321.
R=r, dominik.honnef
CC=golang-dev
https://golang.org/cl/13724043
