ASTM — Section: Section 3.1.6, Fig. 20 - Introduce "EnumTypeDefinition" as a subclass of "TypeDefinition"

Introduce "EnumTypeDefinition" as a subclass of "TypeDefinition", since it is missing from the ASTM specification. It will need to have an association named "definitionType" with "EnumType" that is already present.

The change to specification will be at following places.
At Section# <2.11.2>, page# <50>, line# <6> and section# <3.2.1.3.3.3>, page# <88>, line# <9>, add <TypeDefinition => EnumTypeDefinition>
At Section# <2.11.2>, page# <50>, line# <15>, add <EnumTypeDefinition -> definitionType : EnumType;>
Add a new section# <3.2.1.3.3.3.3>, page# <88>, line# <26> to explain EnumTypeDefinition.
The Figure 20 at section# <3.1.6>, page# <65> will incorporate an appropriate and equivalent change as follows:

Figure 20