Inherits improvement + Validation fixes

[nicksieger]

• Allow @inherits to be used to "typedef" another type/schema, e.g., enums.

Example:

# @model
# @inherits enum<one,two,three>
class MyEnum
end

# @model
# @property [MyEnum] myEnum
class ContainsEnumProperty
end

• Validation fixes. Warns when tags are missing name and/or type that are required in order for the tag to properly generate output.