Add documentation for image.js

[phrfpeixoto]

Please add some documentation on Image.js file.

What is it? In where scenarios i need to include it?

[dmongeau]

You are right, needs documentation.

For now, here is a little explanation. The image.js library is used only to generate URL in javascript. So if you want to create and URL for a 300x300 image you will do something like this:

var img = document.createElement('img');
img.src = Image.url('/path/to/your/image', 300, 300, {
    'crop': true
});

Basically, it's a javascript equivalent of the Image::url() method available in PHP.