window: add simple text tooltip handlers

Using set_transient.

Signed-off-by: Tiago Vignatti <tiago.vignatti@intel.com>
diff --git a/clients/window.h b/clients/window.h
index db232e0..bc0e43a 100644
--- a/clients/window.h
+++ b/clients/window.h
@@ -306,8 +306,15 @@
 const char *
 window_get_title(struct window *window);
 
+int
+widget_set_tooltip(struct widget *parent, char *entry, float x, float y);
+
+void
+widget_destroy_tooltip(struct widget *parent);
+
 struct widget *
 widget_add_widget(struct widget *parent, void *data);
+
 void
 widget_destroy(struct widget *widget);
 void