Add support for multi nested inheritance of the same parent

This request provides the support for nesting the same parent and redefining the parents section several times in the same template.

This allows for instance to reuse a template which defines a container with a content region and nest the containers.

Example:

```javascript
Hogan.compile( '{{<parent}}{{$region}}a{{<parent}}{{$region}}b{{/region}}{{/parent}}{{/region}}{{/parent}}').render({}, {
parent: '...{{$region}}{{/region}}.'
});
```

Will render:

```
...a...b..
```


Basically the compiler associates the nested level to the subs’ code in the generated objects and the template takes into account this level to decide which sub should be used.

This adds also compliance with java implementation that does not fail on these use cases.
I add also three tests in order to demonstrate and test the behavior.

I am using the same template on both server side and ui side, that’s why I need to have this working on both sides.

JB