Add expectAsyncX and expectAsyncUntilX methods, and deprecate the old methods.

README.md

 `test` provides a standard way of writing and running tests in Dart.
 
 * [Writing Tests](#writing-tests)
 * [Running Tests](#running-tests)
   * [Restricting Tests to Certain Platforms](#restricting-tests-to-certain-platforms)
   * [Platform Selectors](#platform-selectors)
   * [Running Tests on Dartium](#running-tests-on-dartium)
 * [Asynchronous Tests](#asynchronous-tests)
 * [Running Tests With Custom HTML](#running-tests-with-custom-html)
 * [Configuring Tests](#configuring-tests)
@@ skipping 325 matching lines @@
 
 ```dart
 import "dart:async";
 
 import "package:test/test.dart";
 
 void main() {
   test("Stream.fromIterable() emits the values in the iterable", () {
     var stream = new Stream.fromIterable([1, 2, 3]);
 
-    stream.listen(expectAsync((number) {
+    stream.listen(expectAsync1((number) {
       expect(number, inInclusiveRange(1, 3));
     }, count: 3));
   });
 }
 ```
 
 [expectAsync]: http://www.dartdocs.org/documentation/test/latest/index.html#test/test@id_expectAsync
 
 ## Running Tests With Custom HTML
 
@@ skipping 306 matching lines @@
 available to tests.
 
 [api]: http://www.dartdocs.org/documentation/test/latest/index.html
 
 The test runner also supports a machine-readable JSON-based reporter. This
 reporter allows the test runner to be wrapped and its progress presented in
 custom ways (for example, in an IDE). See [the protocol documentation][json] for
 more details.
 
 [json]: https://github.com/dart-lang/test/blob/master/doc/json_reporter.md