Add support for demangling __vectors (Nh)

Implements demangling __vector types as per the spec.

```
TypeVector:
    Nh Type
```

Strictly speaking, we should ``test( 'G' );`` before passing down to ``parseType`` because the basetype of vectors should never be anything else.
@yebblies - You don't suppose I'd need to add a ``goto case`` or update this to ``case 'g' .. 'h'`` here would I?

I'm going to make a pull which should add better coverage to the unittests in this module, so would like it to be correct before merge. :)