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/html/htmlwin.h

@@ -260,7 +260,7 @@ public:
 
     // Set HTML page and display it. !! source is HTML document itself,
     // it is NOT address/filename of HTML document. If you want to
-    // specify document location, use LoadPage() istead
+    // specify document location, use LoadPage() instead
     // Return value : false if an error occurred, true otherwise
     virtual bool SetPage(const wxString& source);
 
@@ -503,8 +503,8 @@ protected:
     bool m_makingSelection;
 
 #if wxUSE_CLIPBOARD
-    // time of the last doubleclick event, used to detect tripleclicks
-    // (tripleclicks are used to select whole line):
+    // time of the last double-click event, used to detect triple clicks
+    // (triple clicks are used to select whole line):
     wxMilliClock_t m_lastDoubleClick;
 
     // helper class to automatically scroll the window if the user is selecting