Permit manual menu ordering

_config.yml

@@ -21,6 +21,7 @@ defaults:
     values:
       layout: "page"
       menu: true
+      menu_order: 9
 
 scholar:
   source: .

_includes/header.html

@@ -2,7 +2,7 @@
   <div class="site-masthead">
     <div class="container">
       <nav class="nav">
-        {% assign menu_items = site.pages | where:"menu",true %}
+        {% assign menu_items = site.pages | where:"menu",true | sort:"menu_order" %}
         {% if menu_items.size > 1 %}
         {% for item in menu_items %}
         {% if item.title %}

index.md

 ---
 title: Home
+menu_order: 1
 ---
 The world-wide web is a nearly-ubiquitous and continuously-growing application platform.
 As users increasingly come to depend on web applications, it is more important than ever to be able to make guarantees about these programs.