Add task-list-item class to checkbox lists

According to github-markdown-css, 'task-list-item' class will hide the
bullets on the head of list items.

Closes GH-2.

Author: rhysd

lib/handlers/list-item.js

@@ -32,6 +32,7 @@ function listItem(h, node, parent) {
   var single = (!parent || !parent.loose) && head.children && children.length === 1;
   var result = all(h, single ? head : node);
   var container;
+  var props = {};
 
   if (typeof node.checked === 'boolean') {
     if (!single && head.type !== 'paragraph') {
@@ -49,11 +50,14 @@ function listItem(h, node, parent) {
       checked: node.checked,
       disabled: true
     }));
+
+    /* according to github-markdown-css, this class hides bullet. */
+    props.className = ['task-list-item'];
   }
 
   if (!single && result.length) {
     result = wrap(result, true);
   }
 
-  return h(node, 'li', result);
+  return h(node, 'li', props, result);
 }

test/list-item.js

@@ -50,7 +50,7 @@ test('ListItem', function (t) {
     to(u('listItem', {checked: true}, [
       u('paragraph', [u('text', 'québec')])
     ])),
-    u('element', {tagName: 'li', properties: {}}, [
+    u('element', {tagName: 'li', properties: {className: ['task-list-item']}}, [
       u('element', {
         tagName: 'input',
         properties: {
@@ -70,7 +70,7 @@ test('ListItem', function (t) {
       u('paragraph', [u('text', 'romeo')]),
       u('paragraph', [u('text', 'sierra')])
     ])),
-    u('element', {tagName: 'li', properties: {}}, [
+    u('element', {tagName: 'li', properties: {className: ['task-list-item']}}, [
       u('text', '\n'),
       u('element', {tagName: 'p', properties: {}}, [
         u('element', {
@@ -97,7 +97,7 @@ test('ListItem', function (t) {
     to(u('listItem', {checked: true}, [
       u('html', '<!--tango-->')
     ])),
-    u('element', {tagName: 'li', properties: {}}, [
+    u('element', {tagName: 'li', properties: {className: ['task-list-item']}}, [
       u('text', '\n'),
       u('element', {tagName: 'p', properties: {}}, [
         u('element', {