If no paths are provided, read source from stdin. Fix #165.

lib/src/io.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart_style.src.io;
 
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
 
@@ skipping 42 matching lines @@
 
   var formatter = new DartFormatter(pageWidth: options.pageWidth);
   try {
     var source = file.readAsStringSync();
     var output = formatter.format(source, uri: file.path);
     options.reporter.showFile(file, label, output, changed: source != output);
     return true;
   } on FormatterException catch (err) {
     stderr.writeln(err.message());
   } catch (err, stack) {
-    stderr.writeln('''Hit a bug in the formatter when formatting $label
-  Please report at: github.com/dart-lang/dart_style/issues
+    stderr.writeln('''Hit a bug in the formatter when formatting $label.
+Please report at: github.com/dart-lang/dart_style/issues
 $err
 $stack''');
   }
 
   return false;
 }