movingstd & movingstd2

Occasionally I see a request for computation of a running, windowed standard deviation. This is easily accomplished using filter and the alternative formula for the standard deviation:
std = sqrt((sum(x.^2) - n*xbar.^2)/(n-1)).
movingstd allows you to specify forward, backward or central windows of any desired length. It patches the ends, shortening the window as necessary.
movingstd2 is now included, allowing a moving window standard deviation on 2-dimensional arrays. (I suppose I could easily enough implement movingstdn if that becomes of interest.)