Enums with methods

[yamoling]

Hello,

I was lacking the possibility of having methods and properties to enums, so here is a proposal that adds this functionality. Additionally, the documentation of documented members is now also present in the ".pyi" output.

Here is a summary of the few changes:

• MemberInfo and MemberDef have a doc and a is_property attribute.
• StubInfoBuilder::add_methods adds member properties for enums (but not for classes, the behaviour remains the same)
• StubInfoBuilder::add_methods now looks for struct_id in module.enum_ in addition to module.class.

I would really like these changes to make it to a new release, please let me know if additional changes are required to comply with the current code base.