Rename FooIter to FooIterator.

In some places, there are iterators named like ```FooIter``` while in others its ```FooIterator```.

As of 4e77c1148f0cf702310e5c2cd85b369100ff8ec6, it appears that the ```FooIterator``` style is more commonly used:

```git grep -P '\w+Iter[ ;<]' 4e77c1148f0cf702310e5c2cd85b369100ff8ec6  | wc -l``` = 60
```git grep -P '\w+Iterator[ ;<]' 4e77c1148f0cf702310e5c2cd85b369100ff8ec6  | wc -l``` = 424

So, I renamed all of the instances of ```FooIter``` to ```FooIterator``` since that form appears more common. I also renamed the ```MyIter``` trait to ```MyIterator``` that is used by 2 of the tests for the sake of completeness.