Add a bit to the release notes about dotless identifiers.

notes/2.13.md

@@ -0,0 +1,9 @@
+# Enhancements and Additions
+
+## Dotless identifiers
+
+Previously, objects generated by the library were given id properties with values that contained dots (e.g. "OpenLayers.Control.Navigation_2").  These same identifiers are also used for DOM elements in some case.  Though uncommon, a developer may want to access these elements with a CSS selector.  To facilitate this, we now always generate ids with underscore instead of dot.
+
+Corresponding issues/pull requests:
+
+ * https://github.com/openlayers/openlayers/pull/416