Fix spelling in comments and documentation using codespell

Apply the utility from https://github.com/codespell-project/codespell/
to fix spelling issues in the headers under both include and interface
directories and add a file with a couple of exceptions.

The exact command line used was:

    $ codespell -w -I misc/scripts/codespell.ignore -i 3 in*

include/wx/univ/renderer.h

@@ -360,7 +360,7 @@ public:
     // ------------------
 
     // get the dimensions of the border: rect.x/y contain the width/height of
-    // the left/top side, width/heigh - of the right/bottom one
+    // the left/top side, width/height - of the right/bottom one
     virtual wxRect GetBorderDimensions(wxBorder border) const = 0;
 
     // the scrollbars may be drawn either inside the window border or outside
@@ -397,7 +397,7 @@ public:
 
 #if wxUSE_TEXTCTRL
     // convert between text rectangle and client rectangle for text controls:
-    // the former is typicall smaller to leave margins around text
+    // the former is typically smaller to leave margins around text
     virtual wxRect GetTextTotalArea(const wxTextCtrl *text,
                                     const wxRect& rectText) const = 0;
 

include/wx/univ/scrolbar.h

@@ -131,7 +131,7 @@ protected:
     virtual void DoDraw(wxControlRenderer *renderer) wxOVERRIDE;
     virtual wxBorder GetDefaultBorder() const wxOVERRIDE { return wxBORDER_NONE; }
 
-    // forces update of thumb's visual appearence (does nothing if m_dirty=false)
+    // forces update of thumb's visual appearance (does nothing if m_dirty=false)
     void UpdateThumb();
 
     // SetThumbPosition() helper

include/wx/univ/stdrend.h

@@ -269,7 +269,7 @@ protected:
         // draw complete rectangle
     void DrawRect(wxDC& dc, wxRect *rect, const wxPen& pen);
 
-        // draw the rectange using the first pen for the left and top sides
+        // draw the rectangle using the first pen for the left and top sides
         // and the second one for the bottom and right ones
     void DrawShadedRect(wxDC& dc, wxRect *rect,
                         const wxPen& pen1, const wxPen& pen2);