moment/moment — pull request #1703 by seriousben (2014-06-08 22:07:26+00:00)
Title: Support strings in add and subtract

This adds support for strings on add and subtract.

```javascript
moment().add('1', 'h');
moment().subtract('1', 'h');
moment().add('h', '1');
moment().subtract('h', '1');
```

Notice that the value is a string. At the moment, doing the add would not do anything.