array support

it'd be sweet for this library to support iteration through arrays.

``` js
{ contacts :
  [
    { name : 'matt' },
    { name : 'john' }
  ]
}
```

``` html
<ul>
  {#contacts}<li>{name}</li>{/contacts}
</ul>
```

I took a look at the way the lib is structured - it doesn't look trivial to implement. I feel like it's the last feature missing from a lightweight "core" mustache though.
