Default structure initializer. Sets up default fields. Public fields: name is a tuple of strings specifying the full type name. size is the size of the datatype in bytes, or None if variable-sized. nmemb is 1 for non-list types, None for variable-sized lists, otherwise number of elts. booleans for identifying subclasses, because I can't figure out isinstance().
Reimplemented from xcbgen::xtypes::Type.