Add server-side rendering

I also had to rename the block from core/latest-posts to
core/latestposts since I think there's a bug in the server-side matcher
-- it ignores block comments with hyphens: #882

blocks/library/latest-posts/index.js

@@ -10,7 +10,7 @@ import { registerBlock } from '../../api';
 import { getLatestPosts } from './data.js';
 
 
-registerBlock( 'core/latest-posts', {
+registerBlock( 'core/latestposts', {
 	title: wp.i18n.__( 'Latest Posts' ),
 
 	icon: 'list-view',

blocks/library/latest-posts/index.php

@@ -0,0 +1,37 @@
+<?php
+
+function gutenberg_block_core_latest_posts( $attributes ) {
+	$postsToShow = 5;
+
+	if ( array_key_exists( 'poststoshow', $attributes ) ) {
+		$postsToShow = $attributes['poststoshow'];
+	}
+
+	$recent_posts = wp_get_recent_posts( array(
+		'numberposts' => $postsToShow,
+		'post_status' => 'publish'
+	) );
+
+	$posts_content = '';
+
+	foreach( $recent_posts as $post ) {
+		$post_permalink = get_permalink( $post['ID'] );
+
+		$posts_content .= "<li><a href='{$post_permalink}'>{$post['post_title']}</a></li>\n";
+	}
+
+	$block_content = <<<CONTENT
+<div class="blocks-latest-posts">
+	<ul>
+		{$posts_content}
+	</ul>
+</div>
+
+CONTENT;
+
+	return $block_content;
+}
+
+register_block( 'core/latestposts', array(
+	'render' => 'gutenberg_block_core_latest_posts'
+) );