Figure out way to re-index Algolia crawler when big changes are made

[enriquegh]

When a change like this one happens:
#386

Algolia may be pointing to now non-existent links.
Algolia re-runs the crawler every day but may end up with broken links for ~1 day.

A better solution would be to figure out how different the index will be and if so, re-run the crawler.