.val documentation does not mention the support of numbers.

The API documentation makes mention of string and string[], but not of number for the .val(value) setter. The code explicitly supports numbers:

```
    } else if ( typeof val === "number" ) {
        val += "";
```

This is important because input[type=range] or type=number are always numeric in value, and it's likely someone will be setting the value with a number.
