zeusminer: support added for ZeusMiner scrypt ASICs

--set zus:freq=XYZ (default 328)
--set zus:chips=X (default 6)
--set zus:cores=X (default 8)
--set zus:ignore_golden_nonce (don't check probe response - buggy HW/FW)
nonce_diff is not calculated correctly for scrypt in miner.c...I tried fixing this but this causes a mess of issues because of how the nonce is validated, hash rates displayed, etc, so was much simpler to calculate the diff from target directly.