Ability to browse different versions of the spec

It'd be nice to have a dropdown (or other ability) to change which version of the spec I'm currently browsing, perhaps similar to how the existing LunarG (https://vulkan.lunarg.com/doc/sdk/1.3.243.0/windows/getting_started.html) or Python (https://docs.python.org/3/) docs work.

I'm conflicted on whether this should only support major versions (e.g. 1.2 vs 1.3) or if all released SDK's should be available (e.g. 1.3.329 vs. 1.3.243).

As a bonus: It might be interesting to be able to _diff_ two versions of the spec, or have some other way to very easily see a structured list of changes introduced in a specific version.

The issue names no files, tests, or entry points. Start by resolving whether version selection covers major versions or individual SDK releases, and whether diffing is in scope; done should provide a defined way to browse the selected released spec version and document any limits.

Written by the indexing model from the issue text.