Add .wasParsed() to ArgResults.

pkg/args/lib/src/options.dart

-library options;
-
-import 'package:collection/wrappers.dart';
-
-/// A command-line option. Includes both flags and options which take a value.
-class Option {
-  final String name;
-  final String abbreviation;
-  final List<String> allowed;
-  final defaultValue;
-  final Function callback;
-  final String help;
-  final String valueHelp;
-  final Map<String, String> allowedHelp;
-  final bool isFlag;
-  final bool negatable;
-  final bool allowMultiple;
-  final bool hide;
-
-  Option(this.name, this.abbreviation, this.help, this.valueHelp,
-      List<String> allowed, Map<String, String> allowedHelp, this.defaultValue,
-      this.callback, {this.isFlag, this.negatable, this.allowMultiple: false,
-      this.hide: false}) :
-        this.allowed = allowed == null ?
-            null : new UnmodifiableListView(allowed),
-        this.allowedHelp = allowedHelp == null ?
-            null : new UnmodifiableMapView(allowedHelp) {
-
-    if (name.isEmpty) {
-      throw new ArgumentError('Name cannot be empty.');
-    } else if (name.startsWith('-')) {
-      throw new ArgumentError('Name $name cannot start with "-".');
-    }
-
-    // Ensure name does not contain any invalid characters.
-    if (_invalidChars.hasMatch(name)) {
-      throw new ArgumentError('Name "$name" contains invalid characters.');
-    }
-
-    if (abbreviation != null) {
-      if (abbreviation.length != 1) {
-        throw new ArgumentError('Abbreviation must be null or have length 1.');
-      } else if(abbreviation == '-') {
-        throw new ArgumentError('Abbreviation cannot be "-".');
-      }
-
-      if (_invalidChars.hasMatch(abbreviation)) {
-        throw new ArgumentError('Abbreviation is an invalid character.');
-      }
-    }
-  }
-
-  static final _invalidChars = new RegExp(r'''[ \t\r\n"'\\/]''');
-}