add algolia DocSearch

- closes #73
- uses Algolia free plan with configuration at
  https://github.com/algolia/docsearch-configs/blob/master/configs/mdanalysis.json
- Algolia index is updated every 24 hours.
- NOTE: needed to set site.baseurl to empty to make local testing work;
  according to https://byparker.com/blog/2014/clearing-up-confusion-around-baseurl/
  we do NOT need to use it.

  When running locally my installation failed to load local js and only after
  setting baseurl to empty would it work.
  (See #16 (comment))

_config.yml

@@ -11,7 +11,9 @@ name:             MDAnalysis
 tagline:          A Python package for the analysis of molecular dynamics simulations.
 description:      A Python package for the analysis of molecular dynamics simulations.
 url:              https://www.mdanalysis.org
-baseurl:          /
+# leave baseurl empty,
+# see https://github.com/MDAnalysis/MDAnalysis.github.io/issues/16#issuecomment-385572553
+baseurl:          
 author:
   name:           The MDAnalysis Team
   url:            https://twitter.com/mdanalysis
@@ -65,3 +67,6 @@ twitter:
   url:            https://twitter.com/mdanalysis
 
 
+algolia:
+  index_name: mdanalysis
+  read_only_api_key: 307d780013d06fdde7a4eae462db0e74

_includes/footer.html

@@ -0,0 +1,12 @@
+
+
+<!-- Algolia DocSearch https://community.algolia.com/docsearch/ -->
+<script type="text/javascript" src="https://cdn.jsdelivr.net/npm/docsearch.js@2/dist/cdn/docsearch.min.js"></script> 
+<script type="text/javascript"> docsearch({ 
+apiKey: '{{ site.algolia.read_only_api_key }}', 
+indexName: '{{ site.algolia.index_name }}', 
+inputSelector: 'input[type=text]', 
+debug: true // Set debug to true if you want to inspect the dropdown 
+}); 
+</script>
+

_includes/head.html

@@ -37,6 +37,9 @@
      anchors.add('h1, h2, h3, h4, h5, h6');
      });
   </script>
+
+  <!-- Algolia DocSearch https://community.algolia.com/docsearch/ -->
+  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/docsearch.js@2/dist/cdn/docsearch.min.css" /> 
 
   <!-- Google Analytics -->
   <script>

_includes/sidebar.html

@@ -9,6 +9,8 @@ <h1>
       <p class="lead">{{ site.description }}</p>
     </div>
 
+    <input type="text" class="searchbox" autocomplete="off" name="query" placeholder="Search mdanalysis.org..." />
+
     <nav class="sidebar-nav">
       <a class="sidebar-nav-item{% if page.url == site.baseurl %} active{% endif %}" href="{{ site.baseurl }}/">Home</a>
 

_layouts/default.html

@@ -11,5 +11,6 @@
       {{ content }}
     </div>
 
+    {% include footer.html %}
   </body>
 </html>