add fix vec

Author: tickbh

Diff for: examples/fix_vec.rs

@@ -0,0 +1,9 @@
+use algorithm::FixedVec;
+fn main() {
+    let mut val = FixedVec::new(5);
+    val.insert_head(1);
+    val.insert_head(2);
+    val.insert_head(3);
+    let _ = val.iter_mut().map(|(_, v)| *v = *v * 2).collect::<Vec<_>>();
+    assert_eq!(val.iter().map(|(_, v)| *v).collect::<Vec<_>>(), vec![6, 4, 2]);
+}