Add izip for Python 2/3 compatibility
Add izip for Python 2/3 compatibility

Simply use `izip` from `itertools` on Python 2 and alias `izip` as `zip`
on Python 3. This way an iterable form of `zip` remains available on
both Python 2 and Python 3 that is named `izip`. Should help avoid
having the performance of the two implementations from diverging too
far.

jakirkham/dask-distance