Fix the problem #6 that get the true size for image

Hi, @andrefarzat. I think I found the reason of the problem which we talk about. The image will wrapped by a container when it was loaded, and the largest size of it is the size of the container, so we will get a wrong size if the size of image is larger than the container.

And in the pull request, I create a image in memory and set the `src` for it in the `onMainImageLoad` function, then send it as a param for the `updateCurrentSize` function, then I can get the real size of the image and the real coords. How do you think this? :P