Create GenerateCmd in btcjson v2. Update tests to check GenerateCmd.
Update chaincfg/params.go with a new bool in Params, GenerateSupported,
with true values in SimNetParams and RegressionNetParams and false in
the others.
Create new flag, discreteMining, in CPUMiner struct.
Add GenerateNBlocks function to cpuminer.go and handleGenerate
function to rpcserver.go.
Update documentation for the RPC calls.