Add a `Fast` wrapper class

Provided for convenience, allows `fast` methods to be chained.

```js
var arr = fast([1,2,3,4,5,6]);
var result = arr.filter(function (item) {
  return item % 2 === 0;
});
result instanceof fast; // true
result.length; // 3
```
@megawac hmm. I sort of like the idea of being able to call `new fast.Array([1,2,3])` which leaves room for `new fast.Object({a: 1})` in future. But it really feels wrong, especially because of:
```js
var arr = new fast.Array([1,2,3]);
arr instanceof Array; // true
Array.isArray(arr); // false
```