This brush snaps to day boundaries. When the user releases the brush, the brush fires a brushend event, allowing a listener to adjust the brush extent. Using the new brush transitions released in D3 3.3, the brush smoothly interpolates from the original extent to the rounded extent. Compare this approach to using immediate snapping while brushing.
forked from mbostock's block: Brush resize direction
forked from anonymous's block: Brush resize direction