docs: add copy to clipboard javascript

add popper library for popup menus

docs/layouts/chrome/footer.html

@@ -1,5 +1,5 @@
-
     <script src="/js/jquery.js"></script>
+    <script src="/js/popper.min.js"></script>
     <script src="/js/bootstrap.js"></script>
     <script src="/js/custom.js"></script>
 </body>

docs/static/js/custom.js

@@ -1,14 +1,21 @@
 // Site JS
 
-// Add hover links on headings
 $(function() {
-  return $("h2, h3, h4, h5, h6").each(function(i, el) {
-        var $el, icon, id;
-        $el = $(el);
-        id = $el.attr('id');
-        icon = '<i class="fa fa-link"></i>';
-        if (id) {
-            return $el.prepend($("<a />").addClass("header-link").attr("href", "#" + id).html(icon));
-        }
-    });
+  // Add hover links on headings
+  $("h2, h3, h4, h5, h6").each(function(i, el) {
+    var $el, icon, id;
+    $el = $(el);
+    id = $el.attr('id');
+    icon = '<i class="fa fa-link"></i>';
+    if (id) {
+      return $el.prepend($("<a />").addClass("header-link").attr("href", "#" + id).html(icon));
+    }
+  });
+  // Wire up copy to clipboard buttons
+  $(".copy-to-clipboard").click(function() {
+    var copyText = $(this).prev();
+    copyText.select();
+    document.execCommand("copy");
+    $(this).attr("title", "Copied!");
+  });
 });