Add option for standard node callback convention (err, result)

This pull request is more to show my point, maybe you did not implement it this way for a reason.

I see that you have a way to intentionally send back exceptions:
```javascript
if(err){
    callback(null, 'exception', err);
}else{
    callback({
        success: true,
        data: rows,
        total: rowsTotal[0].totals
    });
}
```

But this is not really in line with the standard node callback(err, results) convention. Why not do:
```javascript
if(err){
    callback(err);
}else{
    callback(null, {
        data: rows,
        total: rowsTotal[0].totals
    });
}
```

This way you might be able to pass the callback to a lot of standard functions directly.
And maybe even automatically set success:true if error is null?

To use this, do:
```javascript
var directCfg = {
    namespace: "ExtRemote",
    apiName: "REMOTING_API",
    apiPath: "/directapi",
    classPath: "/direct",
    classPrefix: "DX",
    relativeUrl: true,
    appendRequestResponseObjects: true,
    conventionalCallbackFormat: true,
    autoSetSuccess: true
};

// Now you can do:
// [...]
read: function(params, callback, sessionID, request, response) {
    models.Foo.findAll({raw: true}).complete(callback);
}
// Instead off
read: function(params, callback, sessionID, request, response) {
    models.Foo.findAll({raw: true}).complete(function(err,results) {
        callback(results);
    });
}
// [...]
```