For most types it was a simple matter of adding #[derive(Debug)] but
ParseOptions needed a manual implementation because the type of
log_syntax_violation is Option<&'a Fn(&'static str)> and Fn doesn't
implement Debug. log_syntax_violation is formatter as Some(Fn(&'static
str)) or None depending upon its value.

Implemented Debug for EncodingOverride as EncodingRef doesn't implement
Debug. Field 'encoding' is formatted as Some(EncodingOverride) or None
based on its value.