Clipping Points and Borders

Hi Eric,

I've done some implementations on KineticJS and I'd like to share it with you.
The main goal with this features is to give a way to do clipping operations independently of its form. So, you can clip an image with a star, triangle or any shape you want. I've added a property to set clip borders too, for a while it's just possible to set width and color border, but I'll implement its style too.

If something doesn't look right, please don't hesitate to talk to me.

Kind Regards,
Felipe Klein Zigmundo