Release versions

[shreevatsa]

Before making this public:

• [x] A page /versions/ that links to several index.html files (chaya-202401.html etc)
  • [x] Manually created
• [x] Say "This is version [N]. Older versions are here" and link to that page.
  • [x] At least, link to the page.
• [x] Code to check that schema versions match (otherwise redirect?)
• [x] Some process for building version files (maybe just before changing schema).
  • [x] Manual instructions in Makefile
• [x] Some message about "use at your own risk, no guarantee of future compatibility, just save this file locally and use it".

[shreevatsa]

Possible improvement: Change make snapshot from a bunch of echo statements to actual code. But we can automate that when needed; closing for now.

[shreevatsa]

More changes done in https://github.com/shreevatsa/chaya/compare/8b755559e93e401cd6a7d7294c3d135e25ac1951...ca7376c0f147e9e328bbe9f7b38a09df49f005ab