The UniqueNode parser and similarly named nodes  

A gotcha with the `UniqueNode` parser is that it doesn't support XML structures that has similarly named nodes within nodes if you want to capture that node name.

It should, however, support XML structures like this:

```xml
<Foo>
  <FooBar>
  </FooBar>
</Foo>
```

There seems to be an issue with it, see #51 