Import refractiveindex.info database

[edmundsj]

I typically use the refractiveindex.info database for doing calculations by hand, and it's an excellent aggregator of academic papers on refractive indices. The entire database is available with files in .yml format, and it should be pretty easy to hook this into the existing code infrastructure. This would be a huge material dataset, and would make this package dramatically more useful to me.

[edmundsj]

#8
This is implemented in the latest pull request from the develop branch. Currently, a test feature until the develop build is fully passing, then it will get merged into master and uploaded to PyPi. In the meantime, available on TestPyPi: https://test.pypi.org/project/rcwa/