ENDF reader File 2 Update

Hey folks!

I implemented some code that reads in unresolved resonance data from File 2's from ENDF files. This is implemented separately from Paul Romano's ENDF reader, though it is in the same module. The overall goal is to integrate the ENDF reader into an abstract structure for nuclear data, which can then be used to (a) manipulate the data or (b) write out to other nuclear data formats. 

Its interface could use a little tweaking; currently, to get to the unresolved resonances of a specific (total spin, L, J) region in an energy range you need to use something like (library).(material)['RxData']['Unresolved'][(index of energy range)][2][(s, l, j)]. This is very clunky, and at the very least could probably be improved by integration with rxname. But at least (to the best of my knowledge) it functions as intended! Any suggestions for improvement would be greatly appreciated :)

-John