Description inheritance of BaseType

[ephrin]

As MSON allows to define Named Base Types with its own descriptions it would be nice to have it available in render result when it used without additional descriptions of property.

Examples follows:

# Data Structures

## hash (string) - a unique identifier

## Entity (object)
+ id: FFFF (hash, sample)

The idea is when rendering of the Entity structure happens I should see description from type definition instead of just only it's real type (string). In case when description is provided for id field of Entity it will override inherited one from type definition.

Thanks.