Hashing API

Here is the Hashing API I have written as part of my GSoC project. PreferredAlgorithms includes all my benchmarks except for Signatures as that requires my SigType enum. Benchmarks are based off of what I found that was already in the codebase. 
> […] since last reset

I don't find a method that allows for resetting, nor one that *specifies* this as a side-effect.