Add StackOverflow social (#243)

data/webpack_assets.json

 {
   "app": {
     "js": "js/app.3fc0f988d21662902933.js",
-    "css": "css/app.d98f2eb6bcd1eaedb7edf166bd16af26.css"
+    "css": "css/app.3f5912c237ddd38c8e76debe081c7ca7.css"
   }
 }

exampleSite/config.toml

   linkedin = ""
   mastodon = ""
   slack = ""
+  stackoverflow = ""
   # 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

 <!-- TODO: Add follow intents where available TODO: Revisit color and hover color -->
 {{ $icon_size := "32px" }}
+{{ with .Param "stackoverflow" }}
+<a href="{{ . }}" target="_blank" class="link-transition stackoverflow link dib z-999 pt3 pt0-l mr1" title="Stack Overflow link" rel="noopener" aria-label="follow on Stack Overflow——Opens in a new window">
+  {{ partial "svg/stackoverflow.svg" (dict "size" $icon_size) }}
+  {{- partial "new-window-icon.html" . -}}
+</a>
+{{ end }}
 {{ with .Param "facebook" }}
 <a href="{{ . }}" target="_blank" class="link-transition facebook link dib z-999 pt3 pt0-l mr1" title="Facebook link" rel="noopener" aria-label="follow on Facebook——Opens in a new window">
   {{ partial "svg/facebook.svg" (dict "size" $icon_size) }}

layouts/partials/svg/stackoverflow.svg

+<svg{{ with .size }} height="{{ . }}" {{ end }}
+    style="enable-background:new 0 0 67 67;"
+    xmlns="http://www.w3.org/2000/svg"
+    viewBox="0 0 24 24"
+    width="{{ .size }}"
+>
+    <path d="M12 0c-6.627 0-12 5.373-12 12s5.373 12 12 12 12-5.373 12-12-5.373-12-12-12zm.869 5.903l3.114 4.567-.975.665-3.115-4.567.976-.665zm-2.812 2.585l4.84 2.838-.6 1.017-4.842-2.838.602-1.017zm-1.276 2.724l5.413 1.521-.291 1.077-5.428-1.458.306-1.14zm-.588 2.461l5.687.569-.103 1.12-5.691-.513.107-1.176zm-.169 2.16h5.835v1.167h-5.835v-1.167zm7.976 3.167h-10v-6h1v5h8v-5h1v6zm.195-8.602l-.945-5.446 1.162-.202.947 5.446-1.164.202z"/>
+</svg>

src/css/_social-icons.css

-.facebook, .twitter, .instagram, .youtube, .github, .gitlab, .linkedin, .medium, .mastodon, .slack {
+.facebook, .twitter, .instagram, .youtube, .github, .gitlab, .linkedin, .medium, .mastodon, .slack, .stackoverflow {
   fill: #BABABA;
 }
 
   fill: #E01E5A;
 }
 
+.stackoverflow:hover {
+  fill: #f48024;
+}

stackbit.yaml

           - type: string
             name: facebook
             label: Facebook
+          - type: string
+            name: stackoverflow
+            label: StackOverflow
           - type: string
             name: twitter
             label: Twitter