debug '-i' option of np command.
java compatible SHA name.
Fix the bug reported following;
  https://github.com/jpmens/mosquitto-auth-plug/issues/29

Comment:
'userdata' is not a context per user in current implementation.
So unpwd_check and acl_check should be processed independently.
impl. superuser_password
Enhance np command:
 it can be given key length with '-k' option.
 it can be given salt length with '-s' option.