Add LinkedIn social share button and add ARIA hidden to Font Awesome icons

- Close #174
- Close #179

_includes/social-share.html

@@ -2,7 +2,12 @@
   {% if site.data.ui-text[site.locale].share_on_label %}
     <h4 class="page__share-title">{{ site.data.ui-text[site.locale].share_on_label }}</h4>
   {% endif %}
-  <a href="https://twitter.com/intent/tweet?text={{ base_path }}{{ page.url }}" class="btn btn--twitter" title="Share on Twitter"><i class="fa fa-twitter"></i><span> Twitter</span></a>
-  <a href="https://www.facebook.com/sharer/sharer.php?u={{ base_path }}{{ page.url }}" class="btn btn--facebook" title="Share on Facebook"><i class="fa fa-facebook"></i><span> Facebook</span></a>
-  <a href="https://plus.google.com/share?url={{ base_path }}{{ page.url }}" class="btn btn--google-plus" title="Share on Google Plus"><i class="fa fa-google-plus"></i><span> Google+</span></a>
-</section><!-- /.social-share -->
+
+  <a href="https://twitter.com/intent/tweet?text={{ base_path }}{{ page.url }}" class="btn btn--twitter" title="{{ site.data.ui-text[site.locale].share_on_label }} Twitter"><i class="fa fa-fw fa-twitter" aria-hidden="true"></i><span> Twitter</span></a>
+
+  <a href="https://www.facebook.com/sharer/sharer.php?u={{ base_path }}{{ page.url }}" class="btn btn--facebook" title="{{ site.data.ui-text[site.locale].share_on_label }} Facebook"><i class="fa fa-fw fa-facebook" aria-hidden="true"></i><span> Facebook</span></a>
+
+  <a href="https://plus.google.com/share?url={{ base_path }}{{ page.url }}" class="btn btn--google-plus" title="{{ site.data.ui-text[site.locale].share_on_label }} Google Plus"><i class="fa fa-fw fa-google-plus" aria-hidden="true"></i><span> Google+</span></a>
+
+  <a href="https://www.linkedin.com/shareArticle?mini=true&url={{ base_path }}{{ page.url }}" class="btn btn--linkedin" title="{{ site.data.ui-text[site.locale].share_on_label }} LinkedIn"><i class="fa fa-fw fa-linkedin" aria-hidden="true"></i><span> LinkedIn</span></a>
+</section>

assets/_scss/_buttons.scss

@@ -121,7 +121,8 @@
   $social:
   (facebook, $facebook-color),
   (twitter, $twitter-color),
-  (google-plus, $google-plus-color);
+  (google-plus, $google-plus-color),
+  (linkedin, $linkedin-color);
 
   @each $socialnetwork, $color in $social {
     &--#{$socialnetwork} {