Add a link to "mastodon" (#159)

* Create fr.toml

French translation

* Social link to "mastodon" added

exampleSite/config.toml

   github = ""
   gitlab = ""
   linkedin = ""
+  mastodon = ""
   # choose a background color from any on this page: http://tachyons.io/docs/themes/skins/ and preface it with "bg-"
   background_color_class = "bg-black"
   featured_image = "/images/gohugo-default-sample-hero-image.jpg"

layouts/partials/social-follow.html

   {{ partial "svg/medium.svg" (dict "size" $icon_size) }}
   {{- partial "new-window-icon.html" . -}}
 </a>
-{{ end }}
+{{ end }}
+{{ with .Param "mastodon" }}
+<a href="{{ . }}" target="_blank" class="link-transition mastodon link dib z-999 pt3 pt0-l mr1" title="Mastodon link" rel="noopener" aria-label="follow on Mastodon——Opens in a new window">
+  {{ partial "svg/mastodon.svg" (dict "size" $icon_size) }}
+  {{- partial "new-window-icon.html" . -}}
+</a>
+{{ end }}

layouts/partials/svg/mastodon.svg

+<svg{{ with .size }} height="{{ . }}" {{ end }} style="enable-background:new 0 0 230 230;" version="1.1" viewBox="0 0 230 230" width="{{ .size }}" xml:space="preserve" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
+<path d="M211.80683 139.0875c-3.1825 16.36625-28.4925 34.2775-57.5625 37.74875-15.16 1.80875-30.0825 3.47125-45.99875 2.74125-26.0275-1.1925-46.565-6.2125-46.565-6.2125 0 2.53375.15625 4.94625.46875 7.2025 3.38375 25.68625 25.47 27.225 46.3925 27.9425 21.115.7225 39.91625-5.20625 39.91625-5.20625l.86875 19.09s-14.77 7.93125-41.08125 9.39c-14.50875.7975-32.52375-.365-53.50625-5.91875C9.23183 213.82 1.40558 165.31125.20808 116.09125c-.36375-14.61375-.14-28.39375-.14-39.91875 0-50.33 32.97625-65.0825 32.97625-65.0825C49.67058 3.45375 78.20308.2425 107.86433 0h.72875c29.66125.2425 58.21125 3.45375 74.8375 11.09 0 0 32.97625 14.7525 32.97625 65.0825 0 0 .4125 37.13375-4.6 62.915" style="fill-rule:evenodd;clip-rule:evenodd;fill:{{ .fill }};"/>
+<path d="M65.68743 96.45938c0 9.01375-7.3075 16.32125-16.3225 16.32125-9.01375 0-16.32-7.3075-16.32-16.32125 0-9.01375 7.30625-16.3225 16.32-16.3225 9.015 0 16.3225 7.30875 16.3225 16.3225M124.52893 96.45938c0 9.01375-7.30875 16.32125-16.3225 16.32125-9.01375 0-16.32125-7.3075-16.32125-16.32125 0-9.01375 7.3075-16.3225 16.32125-16.3225 9.01375 0 16.3225 7.30875 16.3225 16.3225M183.36933 96.45938c0 9.01375-7.3075 16.32125-16.32125 16.32125-9.01375 0-16.32125-7.3075-16.32125-16.32125 0-9.01375 7.3075-16.3225 16.32125-16.3225 9.01375 0 16.32125 7.30875 16.32125 16.3225" fill="#fff"/>
+</svg>

src/css/_social-icons.css

-.facebook, .twitter, .instagram, .youtube, .github, .gitlab, .linkedin, .medium {
+.facebook, .twitter, .instagram, .youtube, .github, .gitlab, .linkedin, .medium, .mastodon {
   fill: #BABABA;
 }
 
 .medium:hover {
   fill: #0077b5
 }
+
+.mastodon:hover {
+  fill: #3088d4;
+}

static/dist/css/app.955516233bcafa4d2a1c13cea63c7b50.css

   margin-bottom: 1em;
 }
 
-.facebook, .twitter, .instagram, .youtube, .github, .gitlab, .linkedin, .medium {
+.facebook, .twitter, .instagram, .youtube, .github, .gitlab, .linkedin, .medium, .mastodon {
   fill: #BABABA;
 }
 
   fill: #0077b5
 }
 
+.mastodon:hover {
+  fill: #3088d4;
+}
+
 /* Put your custom styles here and run `npm start` from the "src" directory on */
 
 #TableOfContents ul li {