Commands which replies -USAGE aren't handled

When executing a command (but just some commands) with the wrong syntax (ex: originate FOOBAR) the reply is neither "+OK" or "-ERR" but instead "-USAGE:". This isn't at all handled (https://github.com/englercj/node-esl/blob/master/lib/esl/Parser.js#L198-L206).

The spec doesn't say anything about that and the API replies aren't really standardised.
I think that we can assume that "-USAGE:" means false for practical reasons.