MAINT: scipy sparse matrix conversion to networkx graph format
MAINT: weighted edges
ENH: speed up some scipy sparse conversions
MAINT: range -> xrange for scipy matrix conversion
MAINT: remove iteritemz, izip, and xrange from networkx scipy sparse conversion
Merge pull request #1226 from argriffing/from-sparse

speed up the conversion from scipy sparse matrix format to networkx graph format