#244 wxWidgets 3.3 compatibility

[Chris Mayo]

I've tried building 1.3.1.0 against wxWidgets 3.3.1. Only one error due to an invalid non-literal msgid:
https://wxwidgets.org/help/msgid-literals/

This seems like the shortest solution and works for me:

--- a/src/xmlcopyeditorcopy.h
+++ b/src/xmlcopyeditorcopy.h
@@ -24,7 +24,7 @@
 #else
 #define FILE_FILTER _("All files (*)|*|XML (*.xml)|*.xml|XHTML (*.html)|*.html|DTD (*.dtd)|*.dtd|XML Schema (*.xsd)|*.xsd|RELAX NG grammar (*.rng)|*.rng|XSL (*.xsl)|*.xsl")
 #endif
-#define ABOUT_COPYRIGHT _(wxString("Copyright © 2005-2022 Gerald Schmidt <gnschmidt@users.sourceforge.net>", wxConvUTF8))
+#define ABOUT_COPYRIGHT _(L"Copyright \u00A9 2005-2022 Gerald Schmidt <gnschmidt@users.sourceforge.net>")
 #define ABOUT_DESCRIPTION _("\nXML Copy Editor is free software released under the GNU\nGeneral Public License.\n\nMany thanks are due to ")
 #define ABOUT_CONTRIBUTORS _T(\
 "Tim van Niekerk, Matt Smigielski,\n"\

In the spirit of the last change to that line:
https://sourceforge.net/p/xml-copy-editor/code/ci/cc16065ac136102094a9c8a24b3b785cc07b971d/

and uses L"" as in the wxWidgets 3.2 docs:
https://docs.wxwidgets.org/3.2/overview_unicode.html

[Zane U. Ji]

Fixed in [40e699]