See bug for more details on exactly what was migrated.
Notably:
* No more Google-internal deployment scripts; see README.godoc-app and
the Makefile for details.
* Build tag "golangorg" is used for the godoc configuration used for
golang.org.
* Use of App Engine libraries replaced with GCP client libraries.
* Redis is used to replace App Engine memcache.
* Google analytics is controlled by an environment variable.
* Regression tests have been migrated from Google-internal.
* hg -> git hash map is moved from Google-internal.
Updates golang/go#27205.
Change-Id: Ia0a983f239c50eda8be2363494c8b784f60c2c6d
Reviewed-on: https://go-review.googlesource.com/133355
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
