rectangle region should support mode='exact'

[pllim]

This gives NotImplementedError:

>>> rect_region.to_mask(mode='exact')

.../regions/shapes/rectangle.py in to_mask(self, mode, subpixels)
    159             use_exact = 1
    160
--> 161         fraction = rectangular_overlap_grid(xmin, xmax, ymin, ymax, nx, ny,
    162                                             self.width, self.height,
    163                                             self.angle.to(u.rad).value,

.../regions/_geometry/rectangular_overlap.pyx in regions._geometry.rectangular_overlap.rectangular_overlap_grid()

NotImplementedError: Exact mode has not been implemented for rectangular apertures

Workaround from @larrybradley for now:

>>> rect_region.to_mask(mode='subpixels', subpixels=32)

[pllim]

Issue 404... 😆 😬