when diff is requested, map is returned (with fallback when data is returned instead)
Small change in DiffNotPossibleException: String cause is now a final field.
Adjusting code to slightly different backend and ajax.
Merge branch 'master' into cleaning-up

Conflicts:
	bin/example_server.dart
	pubspec.yaml
Small modifications (comments, DiffNotPossibleException).
Merge pull request #3 from cleandart/cleaning-up

Cleaning up