Add a wrap sugar function to promises

This adds a function `wrap` that is essentially a sugar method for:

```
var wrapperObject = {};
promise.then(function(value) {
    wrapperObject.key = value;
    return wrapperObject;
});
```

This becomes:

```
var wrapperObject = {};
promise.wrap(wrapperObject, 'key');
```

This function was originally written as a promisehelper function:

https://www.npmjs.org/package/promisehelpers