Type Name as enum instead of object
Rename `Member Type` to `Member`
Rename `Named Type` `base` property to `typeDefinition`
Naming & clarification

- type properties were renamed to class
- made clear distinction between Member Types and other elements of a
Type Section
- Renamed Members to Elements
- use explicit types for Named Types
- flatten Mixing Type
Address review comments
Fix the incorrect class value for One of element
Merge pull request #9 from apiaryio/zdne/ast-feedback

Address Early Adpoter's feedback