C++/Python Binding API

[isaachier]

I've been experimenting using pybind11 to wrap my C++ tracer (https://github.com/isaachier/cpp-client) as a Python tracer. The question I have for this project is whether or not I need to inherit from these classes in order to be opentracing-python compliant. Seeing as Python subclasses are somewhat unnecessary because of Python's duck typing, I'm wondering how far I should pursue subclassing versus just implementing the API without the inheritance.

[isaachier]

Actually, have a way of faking the isinstance check here: pybind/pybind11#1170.