hash-perf-rig

This is a performance test rig for the two main types of hashing we do in NOMS - buzhash and sha1. There's also support for sha256, sha512, and blake2b hash functions for comparison.

As of May 9, these are the numbers I get on a macbook pro 3.1 GHz Intel Core i7.

• no hashing : 3500 MB/s
• sha1 only : 470 MB/s
• sha256 only : 185 MB/s
• sha512 only : 299 MB/s
• blake2b only : 604 MB/s
• bh only : 139 MB/s
• sha1 and bh : 110 MB/s
• sha256 and bh : 80 MB/s
• sha512 and bh : 96 MB/s
• blake2b and bh: 115 MB/s

I think that in the no hashing case there is some compiler optimization going on because I note that if all I do is add a loop that reads out bytes one by one from the slice, it drops to 1000MB/s.

One outcome of this is that there's no sense going to sha256 - we should just jump straight to sha512.