Pixi GrayFilter ported over (thanks nickryall #404)

Fixed Time.totalElapsedSeconds, which gets the other filters working again too.

examples/_site/examples.json

@@ -252,6 +252,10 @@
       "file": "fire.js",
       "title": "fire"
     },
+    {
+      "file": "gray.js",
+      "title": "gray"
+    },
     {
       "file": "lightbeams.js",
       "title": "lightbeams"

examples/filters/gray.js

@@ -0,0 +1,19 @@
+var game = new Phaser.Game(800, 600, Phaser.WEBGL, 'phaser-example', { preload: preload, create: create });
+
+function preload() {
+
+    game.load.image('phaser', 'assets/sprites/phaser2.png');
+    game.load.script('gray', '../filters/Gray.js');
+
+}
+
+function create() {
+
+  var logo = game.add.sprite(game.world.centerX, game.world.centerY, 'phaser');
+  logo.anchor.setTo(0.5, 0.5);
+
+  var gray = game.add.filter('Gray');
+
+  logo.filters = [gray];
+
+}