Correct codes for blake2

[Stebalien]

See: multiformats/multicodec#25

Basically, we had to change the codes as blake2{b,s} are really hash function families, not hash functions.

[ivilata]

I see there are a bunch of values to set, I can either go the boring way and add all 63 entries, or add some loops to do it programmatically with partials on blake2 functions. I'd probably need to use the Enum('<NAME>', <MAPPING>) syntax.