Support multiple devices mining to a single keypair

[Milo123459]

The original Ecl1ipse pool could do this by sending out a different nonce range to each connected miner.

[daralect]

id like this added as well... i have one decent device and two not so decent and put them all on the same keypair and usually when the decent device gets a crappy diff the other two not so great devices make up for it with higher diffs :)