Update crates and added methods to get a key or all keys in an IndexMap

src/lib.rs

@@ -77,6 +77,17 @@ where
             idx
         }
     }
+
+    pub fn key(&self, idx: Index) -> Option<&K> {
+        self.0
+            .iter()
+            .find(|(_, &value)| value == idx)
+            .map(|(key, _)| key)
+    }
+
+    pub fn keys(&self) -> impl Iterator<Item = &K> {
+        self.0.keys()
+    }
 }
 
 impl<K> Default for IndexMap<K>