Cloudflare cache page invalidation

[mgax]

Cloudflare cache invalidation doesn't account for children of index pages, or snippets being used in pages. If the cache max-age is low, this might not be a problem though, but it seems to be set to 4 hours:

% curl -sI https://www.ietf.org/ | grep -i Cache-Control
cache-control: public, max-age=14400

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Copied from #279 (comment).