data implements maps
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 dispose

Conflicts:
	test/collections/filtered_collection_view_test.dart
	test/collections/mapped_collection_view_test.dart
	test/data_collection_test.dart
:wq
:i was ok, just added test. Also realized that onChangeSync listener isn't called imediately after change.
removed unnecesary test
Merge pull request #15 from cleandart/bug/onChangeSync

onChangeSync
Merge branch 'master' into dispose

Conflicts:
	lib/src/data.dart
	test/collections/filtered_collection_view_test.dart