Add Role constructor

theme/theme.go

@@ -18,6 +18,11 @@ type Role struct {
 	Object string
 }
 
+// R is shorthand for creating a Role structure.
+func R (pack, object string) Role {
+	return Role { Package: pack, Object: object }
+} 
+
 // Theme is an object that can apply a visual style to different objects.
 type Theme interface {
 	// Apply applies the theme to the given object, according to the given