Squish image by `scale`. `row_pct`,`col_pct` select focal point of zoom.

def _squish(scale:uniform=1.0, row_pct:uniform=0.5, col_pct:uniform=0.5):
    "Squish image by `scale`. `row_pct`,`col_pct` select focal point of zoom."
    if scale <= 1:
        col_c = (1-scale) * (2*col_pct - 1)
        return _get_zoom_mat(scale, 1, col_c, 0.)
    else:
        row_c = (1-1/scale) * (2*row_pct - 1)
        return _get_zoom_mat(1, 1/scale, 0., row_c)