Updated Dose & SED calculation, added NIST scraper

DoseCalculation.py uses nicer defaults and more clear output.
nist-attenuation-scraper.py is here to scrape some attenuation data from
NIST, so we don't have to rely on pre-saved data on disk, but can load
it from the source each time (probably with caching...)
SurfaceEntranceDoseCalculator.py is now fully in English and with more
pretty output.