Announce that all istl types can now be instantiated with numbers directly

CHANGELOG.md

@@ -17,11 +17,14 @@
 
 - `MultiTypeBlockVector::count()` is now `const`
 
-- The vector class `BlockVector` can now be instantiated with number types
-  directly.  For example, you can now use `BlockVector<double>` instead of
-  the more cumbersome `BlockVector<FieldVector<double,1> >` (The latter
-  still works, though).  A number type is any type for which `Dune::IsNumber<T>::value`
-  is true.
+- All matrix and vector classes can now be instantiated with number types
+  directly (A number type is any type for which `Dune::IsNumber<T>::value`
+  is true).  For example, you can now use `BlockVector<double>` instead of
+  the more cumbersome `BlockVector<FieldVector<double,1> >`.  Similarly, you can use
+  `BCRSMatrix<double>` instead of `BCRSMatrix<FieldMatrix<double,1,1>>`.
+  The old forms still work, and `FieldVector` and `FieldMatrix` types with
+  a single entry can still be cast to their `field_type`.  Therefore, the
+  change is completely backward-compatible.
 
 # Release 2.6