A bit of everything for iterators (#87)

* slight changes functions that use drain

* bug in arrayvec iter

* reverse iter for arrayvec

* nth_back is stable since 1.37

* simpler drain for arrayvec

* soveu forgot to add changed files

* fmt + feature for rustc >= 1.40

* cosmetic changes

* does the ci work now?

* SHNAAAAAAAAATSEEEEEEEEL

tests/arrayvec.rs

@@ -350,3 +350,59 @@ fn ArrayVec_splice() {
   av2.splice(1..=1, Some(4));
   assert_eq!(av2, array_vec![1, 4, 3]);
 }
+
+#[test]
+fn iter_last_nth() {
+  let mut av: ArrayVec<[i32; 10]> = Default::default();
+  av.push(1);
+  av.push(2);
+  av.push(3);
+  av.push(4);
+  assert_eq!(av.len(), 4);
+  let mut iter = av.into_iter();
+  assert_eq!(iter.next(), Some(1));
+  assert_eq!(iter.next(), Some(2));
+  assert_eq!(iter.next(), Some(3));
+  assert_eq!(iter.next(), Some(4));
+  assert_eq!(iter.next(), None);
+  assert_eq!(iter.last(), None);
+
+  let mut av: ArrayVec<[i32; 10]> = Default::default();
+  av.push(1);
+  av.push(2);
+  av.push(3);
+
+  assert_eq!(av.into_iter().nth(0), Some(1));
+}
+
+#[test]
+#[cfg(feature = "rustc_1_40")]
+fn reviter() {
+  let mut av: ArrayVec<[i32; 10]> = Default::default();
+  av.push(1);
+  av.push(2);
+  av.push(3);
+  av.push(4);
+
+  let mut iter = av.into_iter();
+
+  assert_eq!(iter.next(), Some(1));
+  assert_eq!(iter.next_back(), Some(4));
+  assert_eq!(iter.next(), Some(2));
+  assert_eq!(iter.next_back(), Some(3));
+  assert_eq!(iter.next(), None);
+  assert_eq!(iter.next_back(), None);
+
+  let mut av: ArrayVec<[i32; 10]> = Default::default();
+  av.push(1);
+  av.push(2);
+  av.push(3);
+  av.push(4);
+
+  let mut iter = av.into_iter();
+
+  assert_eq!(iter.nth_back(0), Some(4));
+  assert_eq!(iter.nth_back(2), Some(1));
+  assert_eq!(iter.nth_back(0), None);
+  assert_eq!(iter.nth_back(99), None);
+}