Added function that returns the normal tangential velocity gradient for the stokes corner flow with options for slip at the interface and at the walls. Also included an integration function that will integrate the velocity gradient using simpsons rule. Current issues are: no way to match the length scales between macro and stokes because we need the relative slip length to determine the stokes problem, but the slip length will change depending on the relative length scale. Consider matching length scale via momentum. Also secondary interface is observed for most classes of flows