Added full js & js_util packages

packages/quiver_iterables/lib/src/count.dart

 // Copyright 2013 Google Inc. All Rights Reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
 part of quiver.iterables;
 
-/**
- * Returns the concatentation of the input iterables.
- *
- * The returned iterable is a lazily-evaluated view on the input iterables.
- */
-Iterable concat(Iterable<Iterable> iterables) => iterables.expand((x) => x);
+/// Returns an infinite [Iterable] of [num]s, starting from [start] and
+/// increasing by [step].
+Iterable<num> count([num start = 0, num step = 1]) sync* {
+  while (true) {
+    yield start;
+    start += step;
+  }
+}