Fix for #990

[mdklatt]

This PR:

• Adds some basic tests for the localtime module (developed on macOS, test stub added for Windows)
• Fixes #990

All checks are passing except for some unrelated and previously-broken tests:

• [doctest] babel.dates.format_time
• [doctest] babel.dates.get_timezone_name

[codecov[bot]]

Codecov Report

Merging #1006 (deebeb2) into master (95a0ea8) will decrease coverage by 1.34%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1006      +/-   ##
==========================================
- Coverage   90.90%   89.57%   -1.34%     
==========================================
  Files          25       25              
  Lines        4356     4356              
==========================================
- Hits         3960     3902      -58     
- Misses        396      454      +58     

Impacted Files	Coverage Δ
babel/localtime/_unix.py	30.76% <100.00%> (ø)

... and 8 files with indirect coverage changes

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