support for blake2b?

[grexe]

Since there is no recent Java implementation of the 64bit-optimized blake2b variant (which is more common these days), why not support it together with this library? Maybe the project could be merged with the older blake2b project, this would also solve #2 .

Is it all that different or wouldn't it make sense to unify the 2 approaches and select the optimized implementation automatically (via a Java system call or via configuration?