Reduce encoding bytes for level if total number of levels is less than 256

[jimouris]

We're currently using 2 bytes to encode the level:

sha3.update(str(node).encode('ascii') + to_le_bytes(current_level, 2) + next_seed)

This can be abstracted out as a parameter and also detect if the level is less than 256 we can use just a single byte.

[jimouris]

I am closing this as non-important.