splitting code into libraries

diff --git a/pkgs/markdown/lib/markdown.dart b/pkgs/markdown/lib/markdown.dart
index 33d7c37..e2d6a88 100644
--- a/pkgs/markdown/lib/markdown.dart
+++ b/pkgs/markdown/lib/markdown.dart

@@ -5,16 +5,18 @@
 /// Parses text in a markdown-like format and renders to HTML.
 library markdown;
 
-// TODO(rnystrom): Use "package:" URL (#4968).
-part 'src/markdown/ast.dart';
-part 'src/markdown/block_parser.dart';
-part 'src/markdown/html_renderer.dart';
-part 'src/markdown/inline_parser.dart';
+import 'src/markdown/ast.dart';
+import 'src/markdown/block_parser.dart';
+import 'src/markdown/html_renderer.dart';
+import 'src/markdown/inline_parser.dart';
+
+export 'src/markdown/ast.dart';
+export 'src/markdown/inline_parser.dart';
 
 typedef Node Resolver(String name);
 
 /// Converts the given string of markdown to HTML.
-String markdownToHtml(String markdown, {inlineSyntaxes, linkResolver, 
+String markdownToHtml(String markdown, {inlineSyntaxes, linkResolver,
                       bool inlineOnly: false}) {
   final document = new Document(inlineSyntaxes: inlineSyntaxes,
       linkResolver: linkResolver);

diff --git a/pkgs/markdown/lib/src/markdown/ast.dart b/pkgs/markdown/lib/src/markdown/ast.dart
index c966cea..6a05021 100644
--- a/pkgs/markdown/lib/src/markdown/ast.dart
+++ b/pkgs/markdown/lib/src/markdown/ast.dart

@@ -2,7 +2,7 @@
 // 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.
 
-part of markdown;
+library markdown.core;
 
 /// Base class for any AST item. Roughly corresponds to Node in the DOM. Will
 /// be either an Element or Text.

diff --git a/pkgs/markdown/lib/src/markdown/block_parser.dart b/pkgs/markdown/lib/src/markdown/block_parser.dart
index e83bd64..3c20ab8 100644
--- a/pkgs/markdown/lib/src/markdown/block_parser.dart
+++ b/pkgs/markdown/lib/src/markdown/block_parser.dart

@@ -2,7 +2,10 @@
 // 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.
 
-part of markdown;
+library markdown.block_parser;
+
+import 'ast.dart';
+import '../../markdown.dart';
 
 /// The line contains only whitespace or is empty.
 final _RE_EMPTY = new RegExp(r'^([ \t]*)$');

diff --git a/pkgs/markdown/lib/src/markdown/html_renderer.dart b/pkgs/markdown/lib/src/markdown/html_renderer.dart
index 5494394..3d79b7a 100644
--- a/pkgs/markdown/lib/src/markdown/html_renderer.dart
+++ b/pkgs/markdown/lib/src/markdown/html_renderer.dart

@@ -2,7 +2,9 @@
 // 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.
 
-part of markdown;
+library markdown.html_renderer;
+
+import 'ast.dart';
 
 String renderToHtml(List<Node> nodes) => new HtmlRenderer().render(nodes);
 

diff --git a/pkgs/markdown/lib/src/markdown/inline_parser.dart b/pkgs/markdown/lib/src/markdown/inline_parser.dart
index d141659..f74526f 100644
--- a/pkgs/markdown/lib/src/markdown/inline_parser.dart
+++ b/pkgs/markdown/lib/src/markdown/inline_parser.dart

@@ -2,7 +2,10 @@
 // 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.
 
-part of markdown;
+library markdown.inline_parser;
+
+import 'ast.dart';
+import '../../markdown.dart';
 
 /// Maintains the internal state needed to parse inline span elements in
 /// markdown.

diff --git a/pkgs/markdown/test/markdown_test.dart b/pkgs/markdown/test/markdown_test.dart
index 91019fe..29d84a3 100644
--- a/pkgs/markdown/test/markdown_test.dart
+++ b/pkgs/markdown/test/markdown_test.dart

@@ -6,9 +6,7 @@
 library markdownTests;
 
 import 'package:unittest/unittest.dart';
-
-// TODO(rnystrom): Use "package:" URL (#4968).
-import '../lib/markdown.dart';
+import 'package:markdown/markdown.dart';
 
 /// Most of these tests are based on observing how showdown behaves:
 /// http://softwaremaniacs.org/playground/showdown-highlight/