Add tests for two classes with methods #55
Description
We should add an integration test (to integration_tests.rs) which has two structs or classes, each with methods.
If autocxx is behaving right, it will generate the receivers as self: &StructName and cxx will handle it right. If autocxx gets it wrong, they will both be generated as simply self and cxx will barf.
Related comment: dtolnay/cxx#370 (comment)