webdriverjs callbacks should follow the nodejs callback convention

[mreinstein]

http://docs.nodejitsu.com/articles/getting-started/control-flow/what-are-callbacks

The general idea is that the callback is the last parameter. The callback gets called after the function
 is done with all of its operations. Traditionally, the first parameter of the callback is the error value. If
 the function hits an error, then they typically call the callback with the first parameter being an Error 
object. If it cleanly exits, then they will call the callback with the first parameter being null and the rest
 being the return value(s).

[christian-bromann]

I've finally implemented this!

Now each callback gets two parameters. The first one is an error object which could look like this:

{
    status: 7,
    type: "NoSuchElement",
    orgStatusMessage: "An element could not be located on the page using the given search parameters."
}

If there is no error, this parameter is null. The second one is the normal result parameter.
You are also able to pass a callback to each function now. For commands like click (gets no result from the selenium driver) it has the advantage that you are able to check if the command was successful.

[tunix]

@christian-bromann - When is the new release? 👍

[christian-bromann]

@tunix probably this or next week

[tunix]

@christian-bromann - wohoo! :) great news, thanks!