title: While using Fabric lib, how to set a cursor during isDrawingMode to a custom cursor file
body: <p>I use Fabric lib and I want to change the cursor to an external cursor file.
  I usually do it using the canvas CSS by changing the cursor to the url of the cursor file.
  any way to do it in fabric?
  I tried: canvas.freeDrawingCursor = 'url(<a href="http://www.example.com/MyBrush.cur" rel="nofollow">http://www.example.com/MyBrush.cur</a>)'; but it doesn't work.
  any idea?</p>