Add tests for quotefordtd()
Add tests for unimplemented escaping in quotefordtd()
Add tests for unquotefromdtd()
Add tests for unimplemented unescaping in unquotefromdtd()
Add test for entity escaping in regular DTD
Add test for entity escaping roundtrip in regular DTD
Add roundtrip tests for regular DTD
Add and update copyright/license notices
Add documentation about DTD escaping and dialects