Add v0.15.0 doc snapshot and automate process

[johnSchnake]

What this PR does / why we need it:

• Adds script to automate adding a new version of the docs
• Removes the now deprecated docs directory
• Adds docs for v0.15.0 and sets as the newest version of the docs
• Updates the release doc to reference the script that automates
  the addition of a new docs section

Which issue(s) this PR fixes
No formal issue for this; was related to v0.15.0 release.

Special notes for your reviewer:

Release note:

NONE

[johnSchnake]

TODO:

• New page doesnt seem to use the right toc; simple fix
• Footer not updated to link to right docs; simple fix

I didn't want to keep adding content changes here but the ones I included were either fixing an inconsistency (having an extraneous docs directory) or related directly to this automation. However, I want a followup to add:

• We should update part of the readme that links to the docs to link to the doc site instead of the github page. That is the point of the new site to some extent. In addition, I noticed that list is formatted incorrectly and it just runs on in a paragraph instead of actually being a list.

[zubron]

Thanks for fixing up the scripts to work on Linux as well! I've tried it out locally with a fake new version and it all looks good 👍