Allow custom pointStyle size

Allow for users to add in an extra parameter to the label options which changes the size of the legend box separate to the font size. This doesn't affect current functionality, but adds to it.

Author: Alfie Hopkin

src/plugins/plugin.legend.js

@@ -91,7 +91,7 @@ defaults._set('global', {
  */
 function getBoxWidth(labelOpts, fontSize) {
 	return labelOpts.usePointStyle ?
-		fontSize * Math.SQRT2 :
+		(labelOpts.circleSize || fontSize * Math.SQRT2) :
 		labelOpts.boxWidth;
 }
 
@@ -369,7 +369,7 @@ var Legend = Element.extend({
 				if (opts.labels && opts.labels.usePointStyle) {
 					// Recalculate x and y for drawPoint() because its expecting
 					// x and y to be center of figure (instead of top left)
-					var radius = fontSize * Math.SQRT2 / 2;
+					var radius = boxWidth * Math.SQRT2 / 2;
 					var offSet = radius / Math.SQRT2;
 					var centerX = x + offSet;
 					var centerY = y + offSet;