DOC: Migrate from github pages to readthedocs

[mgrover1]

• Py-ART version: All
• Python version: All
• Operating System: All

Description

With moving to Py-ART 2.0 , we should move to readthedocs, similar to the rest of the open radar community xradar/cmweather/etc.

What I Did

Used read the docs and would like documentation previews and such

[mgrover1]

@kmuehlbauer - any suggestions on how to deal with redirects from the previous github pages links?

[kmuehlbauer]

There is something like rediraffe where links can be redirected.

I've always trusted Google to be fast enough to fix it. 😀