Add "Separator" (hr) block to the library.

blocks/library/index.js

@@ -5,3 +5,4 @@ import './image';
 import './text';
 import './list';
 import './quote';
+import './separator';

blocks/library/separator/index.js

@@ -0,0 +1,21 @@
+/**
+ * Internal dependencies
+ */
+import './style.scss';
+import { registerBlock } from 'api';
+
+registerBlock( 'core/separator', {
+	title: wp.i18n.__( 'Separator' ),
+
+	icon: 'minus',
+
+	category: 'common',
+
+	edit() {
+		return <hr className="blocks-separator" />;
+	},
+
+	save() {
+		return <hr />;
+	}
+} );

blocks/library/separator/style.scss

@@ -0,0 +1,4 @@
+.blocks-separator {
+	border: none;
+	border-bottom: 2px solid $light-gray-800;
+}

post-content.js

@@ -12,6 +12,10 @@ window._wpGutenbergPost = {
 			'<p>I imagine prior to the launch of the iPod, or the iPhone, there were teams saying the same thing: the copy + paste guys are <em>so close</em> to being ready and we know Walt Mossberg is going to ding us for this so let\'s just not ship to the manufacturers in China for just a few more weeks… The Apple teams were probably embarrassed. But <strong>if you\'re not embarrassed when you ship your first version you waited too long</strong>.</p>',
 			'<!-- /wp:core/text -->',
 
+			'<!-- wp:core/separator -->',
+			'<hr />',
+			'<!-- /wp:core/separator -->',
+
 			'<!-- wp:core/image -->',
 			'<figure><img src="https://cldup.com/Bc9YxmqFnJ.jpg" /></figure>',
 			'<!-- /wp:core/image -->',