Adding filter transformer and tests.
Updated CL according to comments.
Remove transpose_transformer.dart from charts.dart, it will be checked in the next CL.
Implement charts api v2
Merge pull request #16 from psunkari/charts-api-v2

Implement charts api v2
merge charts.dart

merge charts.dart

Modification base on comments
Merge branch 'filter-transformer' of https://github.com/midoringo8823/charted into filter-transformer

Conflicts:
	lib/charts/charts.dart
	lib/charts/transformers/aggregation_transformer.dart
	lib/charts/transformers/filter_transformer.dart
	test/charts/transformers/aggregation_transformer_test.dart
	test/charts/transformers/chain_transform_test.dart
resolve merge conflicts
Merge pull request #3 from midoringo8823/filter-transformer

Adding filter transformer and tests.
Fix test for the changes on ChartDataObserable -> Observable, changing transformers to extend ChangeNotifier instead of Observable.
Merge pull request #17 from midoringo8823/filter-transformer

Fix test for the changes on ChartDataObserable -> Observable, changing t...
Transpose transformer and test
Change extending Observable to ChangeNotifier
Add transformer tests to the global charted library test.
Add homepage URL in pubspec and add a BUILD file for using pullfrompub to release back into third_party.
Merge pull request #19 from midoringo8823/pubspec_update

Add homepage URL in pubspec and add a BUILD file for using pullfrompub t...
Merge pull request #18 from midoringo8823/transpose_transformer2

Transpose transformer2