Add optional default value for get()

[Kangaroux]

Would be nice to have an optional default parameter for the get function. If the cookie is undefined then the default would be returned instead.

var c = Cookies.get("some-cookie");

if(typeof c === "undefined") {
  c = "default value";
}

vs.

var c = Cookies.get("some-cookie", "default value");

Note that the current implementation uses undefined as the default, so there really is no performance hit from doing this.

https://github.com/ScottHamper/Cookies/blob/master/src/cookies.js#L41