ENH: Added PROJ database metadata to pyproj.show_versions

[snowman2]

• Closes ENH: Expose PROJ database metadata #990
• Tests added
• Fully documented, including history.rst for all changes and api/*.rst for new API

[codecov]

Codecov Report

Merging #992 (63f3c02) into master (3084961) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #992   +/-   ##
=======================================
  Coverage   96.26%   96.26%           
=======================================
  Files          20       20           
  Lines        1765     1766    +1     
=======================================
+ Hits         1699     1700    +1     
  Misses         66       66           

Impacted Files	Coverage Δ
pyproj/_show_versions.py	86.36% <100.00%> (+0.31%)	⬆️

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