Overlays a mask of statistics on an image. By default the
currently displayed figure is overlain.

First, the underlay is converted to RGB. The statistical overlay
is upscaled if necessary (using nearest neighbour sampling) to
match the size of the underlay. Then the RGB data is overlain
with the statmask, without rescaling of the stat values. This
allows for inspection of mask values with the data cursor.

The function returns a handle to the overlay mask if requested.

Notes: Requires freezeColors from the file exchange
Consider using getclim to help set your colormap limits

Usage:
hOv = statmask(stats, [thresh, cmap, clim, cbOpt, hAx])

stats: matrix representing mask values
thresh: scalar value of threshold for transparency (default 0)
cmap: colour-map to use. default flipud(autumn(256))
clim: limits for color display of stats overlay (default min/max of stats)
cbOpt: colorbar display: 'on', 'onwest', or 'hidden', else off (default 'on')
hAx: handle to axes on which to operate (default current axes)

hOv: handle to overlay image is returned

Example:
I = peaks(200);
bwMask = eye(25).*rand(25);
figure;
imshow(I, [], 'Colormap', bone(256), 'InitialMag', 200);
statmask(bwMask);