Option to have each element of an array in matching elements with no wrapper

### Details
This adds an option `unwrappedArrays` which removes the single parent element from arrays, so

```
"elemNames" : [ "one", "two"]
```

with `unwrappedArrays:true` is output as 

```
<elemNames>one</elemNames>
<elemNames>two</elemNames>
```

and with `unwrappedArrays:false` as

```
<elemNames>
    <elemName>one</elemName>
    <elemName>two</elemName>
</elemNames>
```

The `unwrappedArrays` option defaults to false to preserve existing behaviour.

### Motivation
This is intended to be compatible with existing XML systems that expect unwrapped repeated elements