Moved all of the ctypes lib declarations into the mcrt3d.py file and now I import lib wherever it is needed. This seemed a lot cleaner to me.
Added a Rosseland Mean Extinction variable and function to the Dust class (both in C++ and Python).
Added the CPD for random_nu as variables in Dust, and now calculate them in Python and pass them to C++.
Dust::random_nu now uses the pre-calculated CPD values.