fix: allows developers to provide a block pool to argon2

[shawkins]

closes: #1646

Provides a way for developers to reuse memory for argon2. Assumes that the implementation will call allocate / deallocate in pairs - no checking is done for multiple deallocation.

If you are open to this approach, what kind of tests would you like to see for this?

cc @ahus1 @vmuzikar