endftod()

Hi comrades!

After some work and much guidance from Anthony we have sped up the ENDF reader a bit more by circumventing atof() with our own string-to-float converter. This speeds things up by about 40-50%; on my computer I can grab cross-section data in ~8ms now. [This iPython notebook](http://nbviewer.ipython.org/5133015) should still work, and I invite you to check it out!

-John