data implements maps
DataViewMixin removed and functionality moved to DataView
DataCollectionViewMixin removed and functionality moved to DataCollectionView
Merge pull request #9 from cleandart/removeUnnecessaryMixins

Remove unnecessary mixins
Putting _markAdded before .add() and calling beforeAdded stream
Writing tests for DataCollection and ExceptedCollection
Adding more test cases
Adding tests for onBefore
added field author to method clear() in Data
read-only method containsValue moved from Data to DataView
forEarch and putIfAbsent tests simplyfied
merge with master
added empty lines before when, then
Fix tests.
Merge pull request #12 from cleandart/feature/data_collection/on_before

Feature/data collection/on before
Data.fromMap -> Data.from + repaired some bad indentations and whitespaces
merge with master
Merge pull request #11 from cleandart/dataImplementsMap

data implements maps
Merge branch 'master' into feature/removeAll

Conflicts:
	lib/src/data_collection.dart
	test/data_collection_test.dart