feature : zoom

- Created AbstractRenderer in rendering package
- Created CachedRenderer and CachedFrameRenderer to extract basic frame
  caching logic from DrawingController
- Created RendererManager to synchronize updates made to several Renderer
  settings
- Moved FrameRenderer from pskl.rendering to pskl.rendering.frame
- Fixed the resize of the drawing area when the window is resized

js/rendering/AbstractRenderer.js

@@ -0,0 +1,22 @@
+(function () {
+  var ns = $.namespace('pskl.rendering');
+
+  ns.AbstractRenderer = function () {};
+
+  ns.AbstractRenderer.prototype.render =         function (frame)  {throw 'abstract method should be implemented';};
+  ns.AbstractRenderer.prototype.clear =          function ()       {throw 'abstract method should be implemented';};
+
+  ns.AbstractRenderer.prototype.getCoordinates = function (x, y)   {throw 'abstract method should be implemented';};
+
+  ns.AbstractRenderer.prototype.setGridEnabled = function (b)      {throw 'abstract method should be implemented';};
+  ns.AbstractRenderer.prototype.isGridEnabled =  function ()       {throw 'abstract method should be implemented';};
+
+  ns.AbstractRenderer.prototype.setZoom =        function (zoom)   {throw 'abstract method should be implemented';};
+  ns.AbstractRenderer.prototype.getZoom =        function ()       {throw 'abstract method should be implemented';};
+
+  ns.AbstractRenderer.prototype.moveOffset =     function (x, y)   {throw 'abstract method should be implemented';};
+  ns.AbstractRenderer.prototype.getOffset =      function ()       {throw 'abstract method should be implemented';};
+
+  ns.AbstractRenderer.prototype.setDisplaySize = function (w, h)   {throw 'abstract method should be implemented';};
+  ns.AbstractRenderer.prototype.getDisplaySize = function ()       {throw 'abstract method should be implemented';};
+})();