MSON AST reflecting the new specification

For @fosrias, @honzajavorek and @pksunkara to review. 
Those are two different things in the term of where they are in the source MSON file:

```
- property - property inline description
    
    property block description

    - Properties
        - a - a inline description
        - b - b inline description
        - c - c inline description 
```