I'm starting to work on a replacement for Pluto calculations that
are not bounded in time. I'm trying the TOP2013 model that calculates
elliptic parameters of the outer planets Jupiter..Pluto.
I needed to download the 24MB file TOP2013.dat.
I already had redundant download logic for two files, and this was a third.
So I eliminated the redundancy and generalized the download logic
in the new bash function Download.
