Add support for github task lists (aka checkboxes)  actually fixes #268  add color swatch syntax support (#428)

* change source of emojis to github api

* add github checkboxes and color syntax

* update change log

* update extension sets

* correct change log

* clean up, rename color_syntax.dart to color_swatch_syntax.dart

* remove unintentional emoji changes

* restore to master version

* restore to master version

* move ColorSwatchSyntax to gitHubWeb extension set

* add exports for new syntaxes

* made requested changes

* clean up so variables and comments as code review suggested
diff --git a/lib/markdown.dart b/lib/markdown.dart
index 205ba38..6155242 100644
--- a/lib/markdown.dart
+++ b/lib/markdown.dart
@@ -53,12 +53,14 @@
 export 'src/block_syntaxes/list_syntax.dart';
 export 'src/block_syntaxes/long_block_html_syntax.dart';
 export 'src/block_syntaxes/ordered_list_syntax.dart';
+export 'src/block_syntaxes/ordered_list_with_checkbox_syntax.dart';
 export 'src/block_syntaxes/other_tag_block_html_syntax.dart';
 export 'src/block_syntaxes/paragraph_syntax.dart';
 export 'src/block_syntaxes/setext_header_syntax.dart';
 export 'src/block_syntaxes/setext_header_with_id_syntax.dart';
 export 'src/block_syntaxes/table_syntax.dart';
 export 'src/block_syntaxes/unordered_list_syntax.dart';
+export 'src/block_syntaxes/unordered_list_with_checkbox_syntax.dart';
 export 'src/document.dart';
 export 'src/emojis.dart';
 export 'src/extension_set.dart';
@@ -67,6 +69,7 @@
 export 'src/inline_syntaxes/autolink_extension_syntax.dart';
 export 'src/inline_syntaxes/autolink_syntax.dart';
 export 'src/inline_syntaxes/code_syntax.dart';
+export 'src/inline_syntaxes/color_swatch_syntax.dart';
 export 'src/inline_syntaxes/delimiter_syntax.dart';
 export 'src/inline_syntaxes/email_autolink_syntax.dart';
 export 'src/inline_syntaxes/emoji_syntax.dart';