Store iterable range as irange
Store iterable range as irange

Basically pick up `xrange` on Python 2 and `range` on Python 3. So as
not to override a builtin name, store the result to `irange`. This also
makes it clearer how this `range` will behave. Plus it avoids using the
remove `xrange` syntax in Python 3.

dask-image/dask-ndmeasure