docs: Version release plan

[icweaver]

Summary

Starting staging area for packaging newer ANSI C SOFA releases + pure Julia impl

Contacted SOFA board to request tarbarlls

Motivation: Maintain a historical reference for users that is accessible via easy jll builds

2019 - 2023 Release summary

SOFA date	What changed	New routines
2019-07-22	(starting point — what SOFA_jll 2019.7.22+0 ships)	—
2020-07-21	Bug fixes only	none
2021-01-25	Bug and accuracy fixes	none
2021-01-25_a	Small bug-fix patch on top of 2021-01-25	none
2021-05-12	Bug fixes + 3 new routines	iauAtcc13, iauAtccq, iauMoon98
2023-10-11	Bug fixes only (STARPV/PVSTAR machine-precision tweaks, IYV bumped to 2023, comment corrections in A2TF/ATOIQ/C2T06A/FK45Z/FK54Z/HFK5Z/LTPB, t_atccq test fix)	none

The only release with new API surface in this span is 2021-05-12, which adds three routines. All other intermediate releases are bug fixes only, with no signature changes.

Sources:

• ERFA README.rst — "Differences from SOFA"
• ERFA commit b2039ecd "Updating to SOFA 20210512"
• SOFA changes page (2023-10-11 release notes)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.72%. Comparing base (33a841b) to head (015615e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #28   +/-   ##
=======================================
  Coverage   96.72%   96.72%           
=======================================
  Files         245      245           
  Lines        1129     1129           
=======================================
  Hits         1092     1092           
  Misses         37       37           

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