Move a bunch of src/ files into subdirectories.

bin/unittest.dart

Index: bin/unittest.dart
diff --git a/bin/unittest.dart b/bin/unittest.dart
index 3e16498d93d19e1e7cef646300d55efab65a8bb8..9b88fdcd271f0eeabd93ade2a52380bf0746249a 100644
--- a/bin/unittest.dart
+++ b/bin/unittest.dart
@@ -11,11 +11,11 @@ import 'dart:isolate';
 import 'package:args/args.dart';
 import 'package:stack_trace/stack_trace.dart';
 
-import 'package:unittest/src/console_reporter.dart';
-import 'package:unittest/src/exit_codes.dart' as exit_codes;
-import 'package:unittest/src/io.dart';
-import 'package:unittest/src/load_exception.dart';
-import 'package:unittest/src/loader.dart';
+import 'package:unittest/src/runner/console_reporter.dart';
+import 'package:unittest/src/runner/load_exception.dart';
+import 'package:unittest/src/runner/loader.dart';
+import 'package:unittest/src/util/exit_codes.dart' as exit_codes;
+import 'package:unittest/src/util/io.dart';
 import 'package:unittest/src/utils.dart';
 
 /// The argument parser used to parse the executable arguments.