Add basic in-page filter

Fixes #52.

assets/js/base.js

@@ -209,5 +209,28 @@ window.Herman = (function base(Herman, $) {
     $(window).on('resize', fitIframesToContent);
   };
 
+  function filterSiblings(selector, filter) {
+    $(`${selector} ~ section`).each((idx, node) => {
+      if (filter !== '') {
+        if (node.id.includes(filter)) {
+          $(node).show();
+        } else {
+          $(node).hide();
+        }
+      } else {
+        $(node).show();
+      }
+    });
+  }
+  Herman.initializePageFilters = function initializePageFilters() {
+    $('#page-filter').submit(function(event) {
+      event.preventDefault();
+      return false;
+    });
+    $('#page-filter input').keyup(function() {
+      filterSiblings('#page-filter', $('#page-filter input').val());
+    });
+  };
+
   return Herman;
 })(window.Herman || {}, window.jQuery);

assets/js/init.js

@@ -5,6 +5,7 @@ window.Herman = (function init(Herman, $) {
     Herman.initializeToggles();
     Herman.initializeTabs();
     Herman.initializeIframes();
+    Herman.initializePageFilters();
   });
 
   return Herman;

templates/filter_form.j2

@@ -0,0 +1,5 @@
+{% import 'utility.macros.j2' as utility %}
+
+<form id="page-filter">
+    <input placeholder="filter">
+</form>

templates/group.j2

@@ -11,6 +11,7 @@
 {% endblock %}
 
 {% block main %}
+  {% include 'filter_form.j2' %}
   {% for item in items %}
     {% set type = item.context.type %}
     {% include 'item/_item.j2' %}