Add a --reporter flag and expose the expanded reporter.

lib/src/runner/engine.dart

Index: lib/src/runner/engine.dart
diff --git a/lib/src/runner/engine.dart b/lib/src/runner/engine.dart
index 3ddadd5731cc9a936528716b83971750d172f2bf..0513ea2310587e7d3840096afae4972b0826a267 100644
--- a/lib/src/runner/engine.dart
+++ b/lib/src/runner/engine.dart
@@ -80,6 +80,8 @@ class Engine {
   }
 
   /// Creates an [Engine] that will run all tests in [suites].
+  ///
+  /// [concurrency] controls how many suites are run at once.
   Engine(Iterable<Suite> suites, {int concurrency})
       : _liveTestsBySuite = _computeLiveTestsBySuite(suites),
         _pool = new Pool(concurrency == null ? 1 : concurrency);