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/unichar.h

@@ -121,7 +121,7 @@ public:
     wxUint16 LowSurrogate() const { return LowSurrogate(m_value); }
 
     // Conversions to char and wchar_t types: all of those are needed to be
-    // able to pass wxUniChars to verious standard narrow and wide character
+    // able to pass wxUniChars to various standard narrow and wide character
     // functions
     operator char() const { return To8bit(m_value); }
     operator unsigned char() const { return (unsigned char)To8bit(m_value); }