Squashed commit of the following:

commit 79d51b6eea410897551252336032ecec1085a0d4
Author: Dongxu Li <dongxuli2011@gmail.com>
Date:   Tue Jul 8 18:53:57 2014 -0400

    ported triming from ellipse to arc

commit f40757bfa1f736589b368536b5ddb24374c49f32
Author: Dongxu Li <dongxuli2011@gmail.com>
Date:   Sun Jul 6 21:38:47 2014 -0400

    trimBoth tweaking

commit c290653433679f1e1e892e516d182664cdfbdb9a
Author: Dongxu Li <dongxuli2011@gmail.com>
Date:   Sun Jul 6 21:38:33 2014 -0400

    arc: trimming by trimCoord