Adding a count helper to dust that starts at 1 instead of 0.

Adds a new helper to dust - @count

E.g;

```
{#carousel}
     <a href="#" class="m-dot" data-slide"{@count}{.}{/count}">{@count}{.}{/count}</a>
{#carousel}
```

When using {@idx} there are a bunch of situations where the desired behaviour is not obtained due to it being 0-based.

For example, the code above could output the following when using @idx:

```
<a href="#" class="m-dot" data-slide=""></a>
<a href="#" class="m-dot m-active" data-slide="1">1</a>
<a href="#" class="m-dot" data-slide="2">2</a>
```