Versioned documentation

[Breakthrough]

Bug/Issue Description: With the launch of the new www.dvr-scan.com website, we still need to tackle the versioning problem. There should be a way to view old versions of the DVR-Scan documentation when new versions are released.

For the time being the docs can still be accessed through https://dvr-scan.readthedocs.io/en/latest/ which is a mirror of the main website, but also has all previous tags. I'll continue to maintain that workflow until a suitable replacement is made.