obsolete iausofa library

[rmathar]

The directory
https://github.com/sdss/coordio/tree/master/cextern/sofa
is an obsolete version of
https://github.com/liberfa/erfa/tree/master/src

I propse to use the "git subtree" command to replace the obsolete local version and to ensure that the other version (which is known to be maintained actively) is always in use.

Besides: one could get the RPM or Debian packages from
https://build.opensuse.org/package/show/home:rjmathar/iausofa-c
with the zypper or apt command to avoid compiling anything within this module.

[albireox]

Hi @rmathar,

Do you know what are the improvements of the newer versions of SOFA? In principle I don't mind updating it, but I since we only use a few features I feel that doing that manually may be better. I've found that adding subtree or modules ends ad making managing the repository more complicated, and people that clone from source not always follow the instructions to initialise the submodule.

Similarly, I would prefer not to depend on an RPM or external installation because that would make coordIO not easily work on macOS, unless you know of an easy way to install SOFA on Mac. Since SOFA is a very simple pure C library compiling it doesn't seem to be likely to cause errors (assuming one has a basic compiler).

[rmathar]

i) The changes within the IAU SOFA releases are documented in
https://www.iausofa.org/archive.html
ii) To keep the software up-to-date with the upstream release has nothing to do with "RPM" or "external installation" or Macs. The RPM's mean that people can get up-to-date versions of the software by bypassing the obsolete variant maintained here.