Add rstrip encoder for use in %rename.

This is like the strip encoder but strips the symbol's suffix instead
of the prefix.

Examples/test-suite/rename_rstrip_encoder.i

@@ -0,0 +1,15 @@
+%module rename_rstrip_encoder
+
+// strip the Cls suffix from all identifiers
+%rename("%(rstrip:[Cls])s") ""; 
+
+%inline %{
+
+class SomeThingCls {
+};
+
+struct AnotherThingCls {
+    void DoClsXCls() {}
+};
+
+%}