filter articles on frontpage by flag. fixes #9

_includes/post-list-frontpage.html

 	<section class="section  typeset">
 		<ul class="list  list--posts">
-			<!--{% assign frontpage_articles = (site.posts | where: "frontpage" , "true") %}-->
-			{% for page in site.posts limit:10 %}
+			{% assign frontpage_articles = (site.posts | where: "frontpage" , "true") %}
+			{% for page in frontpage_articles limit:10 %}
 				<li class="item  item--post">
 					<article class="article  article--post">