0.28.0-dev.0

https://pub.dev/packages/rxdart/versions/0.28.0-dev.0

Feedback on this change appreciated as this is a dev release before 0.28.0 stable!

ValueStream:
- Add lastEventOrNull getter to ValueStream, which returns the last emitted event (either data/value or error event), or null.
- Add isLastEventValue, isLastEventError and errorAndStackTraceOrNull extension getters to ValueStream, to check the kind of the last emitted event is data/value or error.
- Update documentation.
ReplayStream:
- Add errorAndStackTraces to ReplayStream, which returns a list of emitted ErrorAndStackTraces.
Rename Notification and Kind to better reflect their purpose, and to avoid confusion with Flutter's Notification class.

Feedback on this change appreciated as this is a dev release before 0.28.0 stable!

ValueStream:
- Add lastEventOrNull getter to ValueStream, which returns the last emitted event (either data/value or error event), or null.
- Add isLastEventValue, isLastEventError and errorAndStackTraceOrNull extension getters to ValueStream, to check the kind of the last emitted event is data/value or error.
- Update documentation.
ReplayStream:
- Add errorAndStackTraces to ReplayStream, which returns a list of emitted ErrorAndStackTraces.
Rename Notification and Kind to better reflect their purpose, and to avoid confusion with Flutter's Notification class.