Add Caishen support

Based on information from here: https://bitcointa.lk/threads/ann-p2pool-cai-first-caishen-p2pool.291148/#post-6031449
As no full source was released, rest of values are default, guessed or based on Caishen source.
Until confirmed by thepool.pw it's not sure if it's 100% compatible but seems to work for now.