bugfix (#50): Fix pointer position for older browsers.

Some older webkit browsers give incorrect values for e.clientX/
e.clientY, so switched to using e.pageX - window.pageXOffset,
to get the position relative to the viewport.
bugfix (#49): Redraw when sprite image has loaded.

The canvas was never redrawn when a sprite image had finished
loaded, which caused draw settings like scaling to not be used.
Update version number to 2.2.2.