Increase timeouts for Node.
Be kinder on memory.
Be _even_ kinder on memory...

Given that we are single threaded, we can share our
words array with all competing instances: the hash
function will fail or return but will not be interrupted
Check on H only once
Splitting SHA-256/512 into proper classes.
Reuse buffers.
Accept output buffers
Quicker checks.
Reuse the same buffer for all PBKDF2 operation.
Less timeout, PBKDF2 is faster now.
Run all tests.