BUG: Return multiple authorities with pyproj.crs.CRS.list_authority

[snowman2]

• Tests added
• Fully documented, including history.rst for all changes and api/*.rst for new API

[codecov]

Codecov Report

Merging #943 (c141404) into master (c0ba8be) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #943   +/-   ##
=======================================
  Coverage   96.23%   96.23%           
=======================================
  Files          20       20           
  Lines        1754     1754           
=======================================
  Hits         1688     1688           
  Misses         66       66           

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