about: Support avatars from Gravatar.com (#194)

exampleSite/config.toml

@@ -23,7 +23,8 @@ defaultContentLanguageInSubdir = false
   role = "Professor of Artificial Intelligence"
   organization = "Stanford University"
   organization_url = ""
-  avatar = "portrait.jpg"
+  gravatar = false  # Get your avatar from Gravatar.com? (true/false)
+  avatar = "portrait.jpg"  # Specify an avatar image (in `static/img/` folder) or delete value to disable avatar.
   email = "test@example.org"
   address = "Building 1 Room 1, Stanford University, California, 90210, USA"
   office_hours = "Monday 10:00 to 13:00 or email for appointment"

layouts/partials/widgets/about.html

@@ -6,10 +6,12 @@
   <div class="col-xs-12 col-md-4">
     <div id="profile">
 
-      {{ with $.Site.Params.avatar }}
-      <div class="portrait" style="background-image: url('{{ $.Site.BaseURL }}img/{{ . }}');">
-      </div>
-      <meta itemprop="image" content="{{ $.Site.BaseURL }}img/{{ . }}">
+      {{ if $.Site.Params.gravatar }}
+      <div class="portrait" style="background-image: url('https://s.gravatar.com/avatar/{{ md5 $.Site.Params.email }}?s=200');"></div>
+      <meta itemprop="image" content="https://s.gravatar.com/avatar/{{ md5 $.Site.Params.email }}?s=200">
+      {{ else if $.Site.Params.avatar }}
+      <div class="portrait" style="background-image: url('{{ $.Site.BaseURL }}img/{{ $.Site.Params.avatar }}');"></div>
+      <meta itemprop="image" content="{{ $.Site.BaseURL }}img/{{ $.Site.Params.avatar }}">
       {{ end }}
 
       <div class="portrait-title">