Add quotes to values containing spaces

[ncihnegn]

Because CLI11 will fail to parse an INI file with such values.
To fix #195.

[codecov]

Codecov Report

Merging #198 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #198   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          12     12           
  Lines        1893   1900    +7     
=====================================
+ Hits         1893   1900    +7

Impacted Files	Coverage Δ
include/CLI/StringTools.hpp	100% <100%> (ø)	⬆️
include/CLI/Config.hpp	100% <100%> (ø)	⬆️

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[codecov]

Codecov Report

Merging #198 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #198   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          12     12           
  Lines        1889   1898    +9     
=====================================
+ Hits         1889   1898    +9

Impacted Files	Coverage Δ
include/CLI/StringTools.hpp	100% <100%> (ø)	⬆️
include/CLI/Config.hpp	100% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update bd67a95...e5957b6. Read the comment docs.