API: Undeprecate .scalar_sum()

It's a judgment call; deprecations feel like breaking changes to some
people, so we should be pragmatic about it. Renaming a bunch of methods
in a minor release seems ok (subview and slice methods, they are more
obscure) but we should be careful with widely used API.

Will be deprecated in 0.13

Author: bluss

README.rst

@@ -101,7 +101,8 @@ Recent Changes (ndarray)
   - Rename ``scalar_sum`` to ``sum``, ``subview`` to ``index_axis``,
     ``subview_mut`` to ``index_axis_mut``, ``subview_inplace`` to
     ``collapse_axis``, ``into_subview`` to ``index_axis_move``, and
-    ``slice_inplace`` to ``slice_collapse`` (deprecating the old names).
+    ``slice_inplace`` to ``slice_collapse`` (deprecating the old names,
+    except for ``scalar_sum`` which will be in 0.13).
   - Deprecate ``remove_axis`` and fix soundness hole when removing a zero-length axis.
   - Implement ``Clone`` for ``LanesIter``.
   - Implement ``Debug``, ``Copy``, and ``Clone`` for ``FoldWhile``.

src/numeric/impl_numeric.rs

@@ -47,7 +47,10 @@ impl<A, S, D> ArrayBase<S, D>
     }
 
     /// Return the sum of all elements in the array.
-    #[deprecated(note="renamed to `sum`", since="0.12.1")]
+    ///
+    /// *This method has been renamed to `.sum()` and will be deprecated in the
+    /// next version.*
+    // #[deprecated(note="renamed to `sum`", since="0.13")]
     pub fn scalar_sum(&self) -> A
         where A: Clone + Add<Output=A> + libnum::Zero,
     {