More scaffolding for Link label displays

- Demo: Added option for enabling/disabling argument labels

- Demo: Added bold font import for Nunito

- Links: New CSS classes for controlling the look of Link labels

- Links: New `Label` class for drawing various types of labels on or
around Links. Includes an opaque rectangular background.

- Config: Increased Link slot interval to accommodate argument labels

Author: ZechyW

demo/demo.min.css

@@ -187,13 +187,19 @@ <h5 class="modal-title" id="options-title">Options</h5>
                       Show top links when moving words
                     </label>
                   </div>
-
                   <div class="custom-control custom-checkbox">
                     <input type="checkbox" class="custom-control-input" id="tag-option-bottom-links-on-move">
                     <label class="custom-control-label" for="tag-option-bottom-links-on-move">
                       Show bottom links when moving words
                     </label>
                   </div>
+
+                  <div class="custom-control custom-checkbox mt-3">
+                    <input type="checkbox" class="custom-control-input" id="tag-option-arg-labels">
+                    <label class="custom-control-label" for="tag-option-arg-labels">
+                      Show argument labels on links
+                    </label>
+                  </div>
                 </div>
 
               </div>

demo/demo.min.css.map

@@ -198,6 +198,13 @@ $(async () => {
       );
     });
 
+  const $optionArgLabels = $("#tag-option-arg-labels");
+  $optionArgLabels
+    .prop("checked", uiTag.getOption("showArgLabels"))
+    .on("change", () => {
+      uiTag.setArgLabelVisibility($optionArgLabels[0].checked);
+    });
+
   // --------------------------------------------------------------------------
 
   // The `.exportSvg()` function can be used to save the current

demo/demo.min.js

@@ -63,7 +63,7 @@
 }
 
 // Fonts used in the visualisation
-@import url("https://fonts.googleapis.com/css?family=Nunito:400,600");
+@import url("https://fonts.googleapis.com/css?family=Nunito:400,600,700");
 
 svg, svg text {
   font-family: Nunito, futura, helvetica, arial, sans-serif;