Add a 'Core' category for doc generation.

Change-Id: I56b6b20935f5d543ccf3b9546191203096ed1c47
Reviewed-on: https://dart-review.googlesource.com/58880
Reviewed-by: Kevin Moore <kevmoo@google.com>
Commit-Queue: Devon Carew <devoncarew@google.com>

dartdoc_options.yaml

@@ -1,2 +1,2 @@
 dartdoc:
-  categoryOrder: ["VM", "Web"]
+  categoryOrder: ["Core", VM", "Web"]

sdk/lib/async/async.dart

@@ -88,6 +88,8 @@
  * [futures-tutorial]: https://www.dartlang.org/docs/tutorials/futures/
  * [futures-error-handling]: https://www.dartlang.org/articles/futures-and-error-handling/
  * [test-readme]: https://pub.dartlang.org/packages/test
+ *
+ * {@category Core}
  */
 library dart.async;
 

sdk/lib/collection/collection.dart

@@ -4,10 +4,12 @@
 
 /**
  * Classes and utilities that supplement the collection support in dart:core.
- * 
+ *
  * To use this library in your code:
  *
  *     import 'dart:collection';
+ *
+ * {@category Core}
  */
 library dart.collection;
 

sdk/lib/convert/convert.dart

@@ -50,6 +50,8 @@
  *
  * See the documentation for the [Codec] and [Converter] classes
  * for information about creating your own converters.
+ *
+ * {@category Core}
  */
 library dart.convert;
 

sdk/lib/core/core.dart

@@ -149,6 +149,8 @@
  * The
  * [Dart Language Specification](http://www.dartlang.org/docs/spec/)
  * provides technical details.
+ *
+ * {@category Core}
  */
 library dart.core;
 

sdk/lib/developer/developer.dart

@@ -12,6 +12,7 @@
 ///
 ///     import 'dart:developer';
 ///
+/// {@category Core}
 library dart.developer;
 
 import 'dart:async';

sdk/lib/math/math.dart

@@ -8,6 +8,8 @@
  * To use this library in your code:
  *
  *     import 'dart:math';
+ *
+ * {@category Core}
  */
 library dart.math;
 

sdk/lib/typed_data/typed_data.dart

@@ -8,6 +8,8 @@
 /// To use this library in your code:
 ///
 ///     import 'dart:typed_data';
+///
+/// {@category Core}
 library dart.typed_data;
 
 import "dart:_internal" show UnmodifiableListBase;