Add fallbacks

If we're going to go with hybrid patterns to avoid sprinkling `if (err) return callback(err); ` everywhere I'm not against using names people are familiar with, especially if we're approximating behavior of an existing pattern:

```javascript
function pledge(resolve, reject) {
    return function obligation(err, data) {
        if (err) {
            return reject(err);
        }
        return resolve(data);
    };
}