Let the compiler determine char signedness

[roehling]

Instead of special-casing or assuming a particular signedness, you can
use the boolean expression ((T)(-1) < 0) to determine signedness of an
integer type at compile time.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.96%. Comparing base (54fa780) to head (630bff2).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #454   +/-   ##
=======================================
  Coverage   96.96%   96.96%           
=======================================
  Files          33       33           
  Lines        2703     2703           
=======================================
  Hits         2621     2621           
  Misses         82       82           

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[stotko]

Thanks! LGTM in general subject to some minor points. Could you have a look at these?

[stotko]

LGTM, merging.