Support GitHub Flavored Markdown (#133)

packages/flutter_markdown/example/lib/main.dart

@@ -8,27 +8,67 @@ import 'package:flutter_markdown/flutter_markdown.dart';
 const String _markdownData = """# Markdown Example
 Markdown allows you to easily include formatted text, images, and even formatted Dart code in your app.
 
-## Styling
-Style text as _italic_, __bold__, ~~strikethrough~~, or `inline code`.
+## Titles
 
-- Use bulleted lists
-- To better clarify
-- Your points
+Setext-style
+
+```
+This is an H1
+=============
+
+This is an H2
+-------------
+```
+
+Atx-style
+
+```
+# This is an H1
+
+## This is an H2
+
+###### This is an H6
+```
+
+Select the valid headers:
+
+- [x] `# hello`
+- [ ] `#hello`
 
 ## Links
-You can use [hyperlinks](hyperlink) in markdown
+
+[Google's Homepage][Google]
+
+```
+[inline-style](https://www.google.com)
+
+[reference-style][Google]
+```
 
 ## Images
 
-You can include images:
+![Flutter logo](/dart-lang/site-shared/master/src/_assets/image/flutter/icon/64.png)
 
-![Flutter logo](https://raw.githubusercontent.com/dart-lang/site-shared/master/src/_assets/image/flutter/icon/64.png)
+## Tables
 
-## Markdown widget
+|Syntax                                 |Result                               |
+|---------------------------------------|-------------------------------------|
+|`*italic 1*`                           |*italic 1*                           |
+|`_italic 2_`                           | _italic 2_                          |
+|`**bold 1**`                           |**bold 1**                           |
+|`__bold 2__`                           |__bold 2__                           |
+|`This is a ~~strikethrough~~`          |This is a ~~strikethrough~~          |
+|`***italic bold 1***`                  |***italic bold 1***                  |
+|`___italic bold 2___`                  |___italic bold 2___                  |
+|`***~~italic bold strikethrough 1~~***`|***~~italic bold strikethrough 1~~***|
+|`~~***italic bold strikethrough 2***~~`|~~***italic bold strikethrough 2***~~|
 
-This is an example of how to create your own Markdown widget:
+## Styling
+Style text as _italic_, __bold__, ~~strikethrough~~, or `inline code`.
 
-    Markdown(data: 'Hello _world_!');
+- Use bulleted lists
+- To better clarify
+- Your points
 
 ## Code blocks
 Formatted Dart code looks really pretty too:
@@ -43,15 +83,26 @@ void main() {
 }
 ```
 
+## Markdown widget
+
+This is an example of how to create your own Markdown widget:
+
+    Markdown(data: 'Hello _world_!');
+
 Enjoy!
+
+[Google]: https://www.google.com/
 """;
 
 void main() {
   runApp(MaterialApp(
     title: "Markdown Demo",
     home: Scaffold(
       appBar: AppBar(title: const Text('Markdown Demo')),
-      body: const Markdown(data: _markdownData),
+      body: Markdown(
+        data: _markdownData,
+        imageDirectory: 'https://raw.githubusercontent.com',
+      ),
     ),
   ));
 }