a possible new and faster hash backend

doc/todo/consider_meow_backend.mdwn

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+I recently discovered (thanks to Paul Wise) the [Meow hash][]. The
+TL;DR: is that it's a fast non-crypto hash which might be useful for
+git-annex. Here's their intro, quoted from the website:
+
+[Meow hash]: https://mollyrocket.com/meowhash
+
+> The Meow hash is a high-speed hash function named after the character
+> Meow in [Meow the Infinite][]. We developed the hash function at
+> [Molly Rocket][] for use in the asset pipeline of [1935][].
+> 
+> Because we have to process hundreds of gigabytes of art assets to build
+> game packages, we wanted a fast, non-cryptographic hash for use in
+> change detection and deduplication. We had been using a cryptographic
+> hash ([SHA-1][]), but it was
+> unnecessarily slowing things down.
+> 
+> To our surprise, we found a lack of published, well-optimized,
+> large-data hash functions. Most hash work seems to focus on small input
+> sizes (for things like dictionary lookup) or on cryptographic quality.
+> We wanted the fastest possible hash that would be collision-free in
+> practice (like SHA-1 was), and we didn't need any cryptograhic security.
+> 
+> We ended up creating Meow to fill this niche.
+
+ [1935]: https://molly1935.com/
+ [Molly Rocket]: https://mollyrocket.com/
+ [Meow the Infinite]: https://meowtheinfinite.com/
+ [SHA-1]: https://en.m.wikipedia.org/wiki/SHA-1
+
+I don't an immediate use case for this right now, but I think it could
+be useful to speed up checks on larger files. The license is a
+*little* weird but seems close enough to a BSD to be acceptable.
+
+I know it might sound like a conflict of interest, but I *swear* I am
+not bringing this up only as a oblique feline reference. ;) -- [[anarcat]]