Per type user data

[billyquith]

In v3.0 tags have been removed, however, it is useful to be able to markup the type data. Add ability to associate user data with types, e.g.

Class::declare<HasUserData>()
    .function("foo", &Cls::foo)( UserData("value", 3) )
    .property("value", &Cls::getValue)
     (
         UserData("value", 2.5f),
         UserData("value2", "xyz")
     );

[billyquith]

First pass done.