fixing compatibility with photutils (v1.3.0) and increased precision of magnitudes and zeropoints

[patkel]

Hi developers, I have made edits to imexamine.py that both increase the precision of the magnitude and zeropoint readout (and switch from exponential to float), as well as fix a compatibility issue with photutil v 1.3.0 which is that the Axes argument is not axes=ax instead of ax=ax

Thanks so much for your work on the package! As I mentioned I am trying to set this up for a class.