enmap.submap docs are misleading

[mhasself]

Documentation of submap is misleading. If cdelt has negative elements (and it probably should), then the recommended positions of "ra_min" and "ra_max" will cause the wcs of the output map to have all positive cdelt (which, as readers of my ellipses will not be surprised to learn, I think it should not).

The docstring is a little more clear, using "xfrom" and "xto" instead of min and max.

To avoid confusion it might be helpful if submap had a noflip argument, like subinds does.

[msyriac]

My bad; agreed that "from" and "to" is better, along with possibly adding a note on the negative cdelt convention.
I leave it to you and @amaurea re: adding noflip. I support it.