Radium/Python interoperability

[MathiasPaulin]

Could be very useful to have a python binding of the Radium libraries.

• Allow to load/access/call Radium model and functions from python
• Allow to call Python functions/module/ etc ... from a Radium lib or app.

PyBind11 (https://pybind11.readthedocs.io/en/latest/) seems to be a good tool to use for that as it already supporte interfacing Eigen with Python.

To automate the binding, the Binder project (https://cppbinder.readthedocs.io/en/latest/index.html) generates PyBind11 macro.