I kind of saw a Pivotal object as an instance with a token. Since this is more of a utility method than an instance method, I made it static. I thought it made more sense to do something along the lines of the following:

	Pivotal.getToken(username, password, function(token) {
		var pivotal = new Pivotal(token);
	});

Rather than:

	var pivotal = new Pivotal();
	pivotal.getToken(username, password, function(token) {
		pivotal.useToken(token);
	});

In my mind, a pivotal instance shouldn't be without a token, so to prevent an invalid instance of pivotal, I made the method static. If you disagree, I can change it.