libpyne

This PR makes our C/C++ library a first class citizen following [these suggestions](http://lucumr.pocoo.org/2013/8/18/beautiful-native-libraries/).

This basically entails a complete refactor of the C++ side of the build system.  This has the following features:

* a single `libpyne` that you can link against
* a single `pyne.h` that can be included via `#include "pyne/pyne.h"`

Other features such as those implemented by FindPyne.cmake have all been maintained.  

Testing this feature likely involves blowing away the existing install dir as it is incompatible with the develop install.  I anticipate that this feature will be useful to folks like @makeclean.

For background, I need to do something similar for bright and figured that I'd practice on pyne :)
This is union-equals, like `+=` but for sets not lists