Protocol changes for different K and N parameters

[martin-key]

Hello!
As some of the Equihash PoW based chains are going to change K and N parameters I propose the following change on the stratum protocol:

{"id": 1, "method": "mining.subscribe", "params": ["CONNECT_HOST", CONNECT_PORT, "MINER_USER_AGENT", "SESSION_ID"]}\n
{"id": 1, "result": ["SESSION_ID", "NONCE_1", "K", "N"], "error": null}\n

K and N parameters to be provided in the result of the subscription to the pool. In order to make it compatible with older software these parameters shall be optional. If they are not present the mining software shall consider them as the default 9/200 values.

[h4x3rotab]

I'd like to put N before K:

{"id": 1, "method": "mining.subscribe", "params": ["CONNECT_HOST", CONNECT_PORT, "MINER_USER_AGENT", "SESSION_ID"]}\n
{"id": 1, "result": ["SESSION_ID", "NONCE_1", "N", "K"], "error": null}\n