rpcuser and rpcpassword are deprecated; use rpcauth instead

[achow101]

Instead of setting rpcuser and rpcpassword since they are deprecated, you should use the given username and password to generate the correct rpcauth lines.

[jlopp]

Since I don't want to try to duplicate the python generator script in JS I'm removing the options for simplicity and added documentation about how to generate the auth value in 8738601