Remove all readthedocs pages and setup redirects to docs.cider.mx

[danielcompton]

Once this is merged, we will need to:

• rebuild latest and stable. This should delete all existing
  HTML sources and cause every request to hit the RTD servers. Then those
  requests will get a 302 redirect to their new counterpart on docs.cider.mx.
• request RTD staff to change our 302 temporary redirects to 301
  redirects. This seems like a manual process

  Users can request a 301 redirect via our support queue and we just need to make a change on those redirects after they set them up and are happy.

Fixes #2695.

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[danielcompton]

I've rebuilt the latest and stable docs. I had to quickly create a tag 0.23.1 to rebuild stable, which I've now removed.