more iterators and relax trait bounds

What's Changed

• Added implementations for IntoIter and IterMut by @TinBryn in #16
• <N: Clone> bound is not required on {Add,Sub}{,Assign} by @samueltardieu in #17
• Cleanup redundant references by @samueltardieu in #18

New Contributors

• @TinBryn made their first contribution in #16
• @samueltardieu made their first contribution in #17

Full Changelog: v0.5.2...v0.5.3