Demonstrate call tip clicks in the stc sample

This adds a demonstration of handling call tip clicks to the stc sample.
Instead of showing a single call tip, 3 different call tips can be
shown. The sample demonstrates how to move between the call tips
depending on if the up or down button was clicked in the call tip
window.

samples/stc/edit.h

@@ -105,9 +105,13 @@ public:
     // stc
     void OnMarginClick (wxStyledTextEvent &event);
     void OnCharAdded  (wxStyledTextEvent &event);
+    void OnCallTipClick(wxStyledTextEvent &event);
 
     void OnKeyDown(wxKeyEvent &event);
 
+    // call tips
+    void ShowCallTipAt(int position);
+
     //! language/lexer
     wxString DeterminePrefs (const wxString &filename);
     bool InitializePrefs (const wxString &filename);
@@ -137,6 +141,9 @@ private:
     int m_FoldingMargin;
     int m_DividerID;
 
+    // call tip data
+    int m_calltipNo;
+
     wxDECLARE_EVENT_TABLE();
 };