chrono support

I saw [custom_get_data.rs](https://github.com/Koka/odbc-rs/blob/77af3cd03ba5bc673b8d23676ec1fa8695e8e625/examples/custom_get_data.rs) but would it be possible to have native Chrono support?

I'm thinking maybe it's not since ODBC can be used to query different sources which probably use differents datetime formats.