Fix updating of layer dimension labels. (alexlenail#5)

* Fix updating of layer dimension labels.

When using the numeric range controls to alter the width of the
layers, the input labels weren't being updated in the diagram.

Address by creating the corresponding d3.js elements initially, but
then updating their dynamic properties on change.

Also fix a rendering glitch when superscripting dimensions with
repeated digits, e.g., "11".

* Limit scope, update text label elements only.

index.html

@@ -312,7 +312,9 @@ <h4>Architecture:</h4>
 var showBias = false;
 
 var showLabels = true;
-let sup = (s) => s.replace('0','⁰').replace('1','¹').replace('2','²').replace('3','³').replace('4','⁴').replace('5','⁵').replace('6','⁶').replace('7','⁷').replace('8','⁸').replace('9','⁹')
+let sup_map = {'0': '⁰', '1': '¹', '2': '²', '3': '³', '4': '⁴', '5': '⁵', '6': '⁶', '7': '⁷', '8': '⁸', '9': '⁹'};
+let sup = (s) => Array.prototype.map.call(s, (d) => (d in sup_map && sup_map[d]) || d).join('');
+
 let textFn = (layer_index, layer_width) => ((layer_index === 0 ? "Input" : (layer_index === architecture.length-1 ? "Output" : "Hidden")) + " Layer ∈ ℝ" + sup(layer_width.toString()));
 var nominal_text_size = 12;
 var textWidth = 70;
@@ -365,16 +367,13 @@ <h4>Architecture:</h4>
                .merge(node);
 
     text = text.data(label);
-    text.exit().remove();
-    text = text.enter()
-               .append("text")
-               .text(function (d) { return (showLabels ? d.text : ""); })
-               .attr("class", "text")
+    if (text.empty())
+        text = text.enter().append("text").attr("class", "text");
+    text = text.text(function (d) { return (showLabels ? d.text : ""); })
                .attr("dy", ".35em")
                .style("font-size", nominal_text_size+"px")
                .merge(text);
 
-
     $('#count span:first').text(graph.nodes.length+" nodes, "+graph.links.length+" edges you don't need to draw yourself! ")
     redistribute();
 }