Also add a From implementation for &mut Option<T> -> `Option<&mut T>'

Author: weiznich

src/libcore/option.rs

@@ -1071,6 +1071,13 @@ impl<'a, T> From<&'a Option<T>> for Option<&'a T> {
     }
 }
 
+#[stable(feature = "option_ref_from_ref_option", since = "1.30.0")]
+impl<'a, T> From<&'a mut Option<T>> for Option<&'a mut T> {
+    fn from(o: &'a mut Option<T>) -> Option<&'a mut T> {
+        o.as_mut()
+    }
+}
+
 /////////////////////////////////////////////////////////////////////////////
 // The Option Iterators
 /////////////////////////////////////////////////////////////////////////////