This should get test-documentation and test-help-documentation passing
again after we moved everything around in the last commit.
There are a lot more absolute links (generally in code comments) to
update, but they are lower-priority and can be done in a follow-up
pass.
This commit allows for the /api-new/ page to rendered similarly to our
/help pages. It's based on the old content for /api, but we're not
replacing the old content yet, to give a bit of time to restructure
things reasonably.
Tweaked by eeshangarg and tabbott.