Moved the Option class to its own file in anticipation of working on it.

pkg/args/lib/args.dart

Index: pkg/args/lib/args.dart
diff --git a/pkg/args/lib/args.dart b/pkg/args/lib/args.dart
index 3898b9fd1aafdbb0b778b8d1f9b6be8f20170b74..9e6252a5a2b681ffba321741056ddd25183cc852 100644
--- a/pkg/args/lib/args.dart
+++ b/pkg/args/lib/args.dart
@@ -257,6 +257,8 @@ library args;
 
 import 'src/parser.dart';
 import 'src/usage.dart';
+import 'src/options.dart';
+export 'src/options.dart';
 
 /**
  * A class for taking a list of raw command line arguments and parsing out
@@ -377,52 +379,6 @@ class ArgParser {
 }
 
 /**
- * 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 Map<String, String> allowedHelp;
-  final bool isFlag;
-  final bool negatable;
-  final bool allowMultiple;
-
-  Option(this.name, this.abbreviation, this.help, this.allowed,
-      this.allowedHelp, this.defaultValue, this.callback, {this.isFlag,
-      this.negatable, this.allowMultiple: false}) {
-
-    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"'\\/]''');
-}
-
-/**
  * The results of parsing a series of command line arguments using
  * [ArgParser.parse()]. Includes the parsed options and any remaining unparsed
  * command line arguments.