Update the PyArrayIterator examples in the README to show `iitems()` & `mitems()` iterators.
Update the PyArrayIterator examples in the README to show `iitems()` & `mitems()` iterators.

Also, the `items()` iterator now yields values of T rather than PyArrayIter[T] instances.

jboy/nim-pymod,jboy/nim-pymod,jboy/nim-pymod,jboy/nim-pymod