add more wrappers

[twmr]

There are a lot of mie codes available in the scatterlib wiki:
https://code.google.com/p/scatterlib/wiki/Spheres . It would be nice if some those codes (especially multiple spheres codes) were wrapped in py-mie.

[darothen]

This would make a really great project. It's fallen outside of my research focus, but I'd certainly endorse somebody using this project as a scaffold to incorporate a variety of scattering codes. I only made this as a test project for practicing library building with travis-ci.