footprint() method returns coordinates in different order than the forward transform

[jdavies-st]

So this isn't a bug, but more of a user interface inconsistency.

For a simple imaging WCS, I might create and call it like so:

...
wcs = gwcs.WCS(...args)
wcs.bounding_box = ((xlow, xhigh), (ylow, yhigh))

x, y = gwcs.wcstools.grid_from_bounding_box(wcs.bounding_box)
ra, dec = wcs(x, y)

So I create a grid of (x, y) points in pixel coords in my image, and get the output (ra, dec) in sky coordinates to which they map.

But the wcs.footprint() method works like the following:

ra, dec = wcs.footprint().T

I.e. the ordering of the return values from the footprint() method is the transpose of that from the forward and reverse transforms. And also it is a single numpy array, instead of a tuple of arrays as in the former.