Array Mapping

The script:

```
var o2 = {
  foo : [1, 2, 3]
};

console.log(json2xml(o2 ));
```

produces:

```
<foo>123</foo>
```

Arrays should be mapped to a sequence like:

```
<foo>
  <item>1</item>
  <item>2</item>
  <item>3</item>
</foo>
```

or 

```
<foo>1 2 3</foo>
```
