Start on Creating Plugins documentation.

Change-Id: Ic75775473cfb405cee5c53b2dc24144dba51a25c
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@nokia.com>

doc/api/examples/exampleplugin/exampleconstants.h

@@ -0,0 +1,14 @@
+#ifndef EXAMPLECONSTANTS_H
+#define EXAMPLECONSTANTS_H
+
+namespace Example {
+namespace Constants {
+
+const char ACTION_ID[] = "Example.Action";
+const char MENU_ID[] = "Example.Menu";
+
+} // namespace Example
+} // namespace Constants
+
+#endif // EXAMPLECONSTANTS_H
+