Sort kernelrelease fact

[ArthurWuTW]

solve issue #731

• implement natural sorting for fact=kernelrelease
• create a sorter_map with key=fact and value=sorter type, now having (kernelrelease, natural) and (uptime, natural-time-delta)
• remove natural_time_delta_sort flag

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.89%. Comparing base (52c0396) to head (cbe67d3).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1139      +/-   ##
==========================================
+ Coverage   76.87%   76.89%   +0.02%     
==========================================
  Files          20       20              
  Lines        1310     1307       -3     
==========================================
- Hits         1007     1005       -2     
+ Misses        303      302       -1     

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