Features
- Added methods to DateTime/NaiveDateTime to present the stored value as a number of nanoseconds since the UNIX epoch (@HarkonenBade #247)
- Added a serde serialise/deserialise module for nanosecond timestamps. (@HarkonenBade #247)
- Added "Permissive" timezone parsing which allows a numeric timezone to be specified without minutes. (@quodlibetor #242)