Calculation of obj.Std not implemented for 2018b and older versions

[why-fi]

https://github.com/Sequynth/Draw/blob/6f555a030e17cc974ba7a37ab69ec2a0d629c5a9/Draw.m#L308

Missing implementation of cleverStd results in impossibility of windowing the image.

Matlab 2018b

[why-fi]

Error in Draw>@(varargin)obj.draggingFcn(varargin{:}) (line 1001)
                        obj.f.WindowButtonMotionFcn = {@obj.draggingFcn, callingAx, Pt, sCenter, sWidth, cStep, wStep};
 
Error while evaluating Figure WindowButtonMotionFcn.