Add support for a global configuration file.

lib/src/runner/configuration.dart

Index: lib/src/runner/configuration.dart
diff --git a/lib/src/runner/configuration.dart b/lib/src/runner/configuration.dart
index 5a3229e0dbfcfb848e65bb6fe3df2877bf31098e..bf21b0932a4f8888e37fd34ecb344bc013958e47 100644
--- a/lib/src/runner/configuration.dart
+++ b/lib/src/runner/configuration.dart
@@ -227,9 +227,13 @@ class Configuration {
 
   /// Loads the configuration from [path].
   ///
+  /// If [global] is `true`, this restricts the configuration file to only rules
+  /// that are supported globally.
+  ///
   /// Throws an [IOException] if [path] does not exist or cannot be read. Throws
   /// a [FormatException] if its contents are invalid.
-  factory Configuration.load(String path) => load(path);
+  factory Configuration.load(String path, {bool global: false}) =>
+      load(path, global: global);
 
   factory Configuration({
       bool help,