Expose PixelArray constructor

lib/canvas.js

@@ -13,6 +13,7 @@ var canvas = require('../build/default/canvas')
   , Canvas = canvas.Canvas
   , Image = canvas.Image
   , cairoVersion = canvas.cairoVersion
+  , PixelArray = Canvas.PixelArray
   , Context2d = require('./context2d')
   , PNGStream = require('./pngstream')
   , fs = require('fs');
@@ -41,6 +42,7 @@ exports.cairoVersion = cairoVersion;
 
 exports.Context2d = Context2d;
 exports.PNGStream = PNGStream;
+exports.PixelArray = PixelArray;
 exports.Image = Image;
 
 /**