Refactorize some stuff to make `dherkin_base.dart` io-agnostic so it can be imported in a browser app.
Refactored most of the private global variables in favor of dependency injection.
Change worker dependency URI to public.
Big Merge BROKEN : Illegal argument on isolate message (object is a closure)
Big Merge OK.
- Less global vars
- dherkin_core does not depend on dart:io
- Cleanup
Cleanup.
Cleanup.
Merge remote-tracking branch 'upstream/master' into big_merge_clean

Conflicts:
	example/run.dart
	lib/dherkin.dart
	lib/src/gherkin_model.dart
	lib/src/gherkin_parser.dart
	lib/src/outputter.dart
	pubspec.yaml
Cleanup.
merging antoine