NSE

Hey Evan - I added a few things that enable me to create an opacity table using the Helmholtz EOS and simple 3-species NSE. It's not the most elegantly coded, but it does the trick. Let me know what you think - if something doesn't belong, is structured stupidly, etc.

* Some slight restructuring to make using the EOS more modular
* included simple n,p,alpha NSE solver for use by the Helmholtz EOS, according to Evan/Rodrigo's suggestions