Moved docgen out of the sdk into pkg/

pkg/docgen/bin/docgen.dart

 /**
  * The docgen tool takes in a library as input and produces documentation
  * for the library as well as all libraries it imports and uses. The tool can
  * be run by passing in the path to a .dart file like this:
  *
  *   ./dart docgen.dart path/to/file.dart
  *
  * This outputs information about all classes, variables, functions, and
  * methods defined in the library and its imported libraries.
  */
 library docgen;
 
 import 'dart:io';
 import 'dart:async';
-import 'lib/dart2yaml.dart';
-import 'lib/src/dart2js_mirrors.dart';
+import '../lib/dart2yaml.dart';
+import '../lib/src/dart2js_mirrors.dart';
 import 'package:markdown/markdown.dart' as markdown;
-import '../../../../pkg/args/lib/args.dart';
-import '../compiler/implementation/mirrors/mirrors.dart';
-import '../compiler/implementation/mirrors/mirrors_util.dart';
+import '../../args/lib/args.dart';
+import '../../../sdk/lib/_internal/compiler/implementation/mirrors/mirrors.dart';
+import '../../../sdk/lib/_internal/compiler/implementation/mirrors/mirrors_util.dart';
 
 /**
  * Entry function to create YAML documentation from Dart files.
  */
 void main() {
   // TODO(tmandel): Use args library once flags are clear.
   Options opts = new Options();
   Docgen docgen = new Docgen();
   
   if (opts.arguments.length > 0) {
     List<Path> libraries = [new Path(opts.arguments[0])];
-    Path sdkDirectory = new Path("../../../");
+    Path sdkDirectory = new Path("../../../sdk/");
     var workingMirrors = analyze(libraries, sdkDirectory, 
         options: ['--preserve-comments', '--categories=Client,Server']);
     workingMirrors.then( (MirrorSystem mirrorSystem) {
       var mirrors = mirrorSystem.libraries.values;
       if (mirrors.isEmpty) {
         print("no LibraryMirrors");
       } else {
         docgen.libraries = mirrors;
         docgen.documentLibraries();
       }
@@ skipping 307 matching lines @@
   if (!dir.existsSync()) {
     dir.createSync();
   }
   File file = new File('docs/$filename');
   if (!file.exists()) {
     file.createSync();
   }
   file.openSync();
   file.writeAsString(text);
 }