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

pkg/sequence_zip/lib/sequence_zip.dart

Index: pkg/sequence_zip/lib/sequence_zip.dart
diff --git a/pkg/sequence_zip/lib/sequence_zip.dart b/pkg/sequence_zip/lib/sequence_zip.dart
index 2f0d7e6c4fd02a48efb8c41b0888fc0f54699989..9863a30ae3a1cbbc334dbf381c2fb0b6254cfa4b 100644
--- a/pkg/sequence_zip/lib/sequence_zip.dart
+++ b/pkg/sequence_zip/lib/sequence_zip.dart
@@ -3,15 +3,11 @@
 // BSD-style license that can be found in the LICENSE file.
 
 /**
- * Utilities for combining multiple streams or Iterables
- * into a single stream or Iterable, respectively.
- *
- * This library defines no new APIs.
- * It's a convenience library for using the APIs in the
- * [iterable_zip](#iterable_zip) and
- * [stream_zip](#stream_zip) libraries.
+ * Please use the libraries `package:collection/iterable_zip.dart` for iterable zipping
+ * or `package:async/stream_zip.dart` for stream zipping.
  */
+@deprecated
 library sequence_zip;
 
-export "iterable_zip.dart";
-export "stream_zip.dart";
+export "iterable_zip";
+export "stream_zip";