Create associated packages for the dart:collection and dart:async libs.

pkg/typed_data/README.md

Index: pkg/typed_data/README.md
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+Helper libraries for working with typed data lists.
+
+The `typed_data` package contains utility functions and classes that makes working with typed data lists easier.
+
+## Using
+
+The `typed_data` package can be imported as
+
+    import 'package:typed_data/typed_data.dart';
+
+## Typed buffers: Growable typed data lists
+
+Typed buffers are contains growable lists backed by typed arrays.
+These are similar to the growable lists returned by `new List()`, 
+but stores typed data like a typed data list.