Initial commit of x-ray data compilation for ensdf.py
support experimental conversion electron data and data missing k conversion electron data
get mednew from nndc instead of local resource and only catch ValueError
Don't use .keys() to check for key in dict
use nucname.znum and use a continue to reduce indentation
remove all redundant try clauses
Fix issues so all ensdf files can be successfully parsed
 _to_id except now catches RuntimeError
combine _getvalue and _to_float
Only download mednew.dat once

Also gets rid of except clause in _to_id because there was only a
single problematic case `1NN`
Update test_ensdf.py with X-ray data
Update and re-arrange docs per @scopatz's suggestions
Merge branch 'ensdf' of https://github.com/crbates/pyne into crbates-ensdf