Support dashed series lines.

This follows on from #68. Unfortunately the dashes jump back and forth
during rendering, which is quite visually annoying. Fixing this would be
quite difficult I suspect.

builder/index.html

@@ -119,7 +119,8 @@
 
           if (typeof(a[key]) === 'object') {
             if (a[key] instanceof Array) {
-              // ignore arrays
+              if (!(b[key] instanceof Array) || a[key].length !== b.length && a[key].length)
+                result[key] = a[key];
             } else {
               var sub = difference(a[key], b[key]);
               if (Object.keys(sub).length)
@@ -411,6 +412,17 @@
           propertyName: 'interpolation',
           values: ['bezier', 'linear', 'step']
         });
+        bindCheckBox({
+          target: chart.seriesSet[0].options,
+          name: 'Use dashed line',
+          propertyName: 'lineDash',
+          convert: function (checked) {
+            return checked ? [5,5] : [];
+          },
+          convertBack: function (value) {
+            return value && value.length ? true : false;
+          }
+        });
 
         // Grid lines
         startControlSection('Grid Lines');

smoothie.d.ts

@@ -13,6 +13,7 @@ export interface ITimeSeriesPresentationOptions {
     strokeStyle?: string;
     fillStyle?: string;
     lineWidth?: number;
+    lineDash?: number[];
 }
 
 export declare class TimeSeries {

smoothie.js

@@ -346,7 +346,8 @@
 
   SmoothieChart.defaultSeriesPresentationOptions = {
     lineWidth: 1,
-    strokeStyle: '#ffffff'
+    strokeStyle: '#ffffff',
+    lineDash: []
   };
 
   /**
@@ -358,7 +359,8 @@
    * {
    *   lineWidth: 1,
    *   strokeStyle: '#ffffff',
-   *   fillStyle: undefined
+   *   fillStyle: undefined,
+   *   lineDash: []
    * }
    * </pre>
    */
@@ -698,6 +700,7 @@
       // Set style for this dataSet.
       context.lineWidth = seriesOptions.lineWidth;
       context.strokeStyle = seriesOptions.strokeStyle;
+      context.setLineDash(seriesOptions.lineDash || []);
       // Draw the line...
       context.beginPath();
       // Retain lastX, lastY for calculating the control points of bezier curves.