Replace cxxopts with cmdline

[zhiqwang]

Resolve #135

[codecov]

Codecov Report

Merging #137 (f4553fb) into master (ec5464d) will not change coverage.
The diff coverage is n/a.

❗ Current head f4553fb differs from pull request most recent head ab79400. Consider uploading reports for the commit ab79400 to get more accurate results

@@           Coverage Diff           @@
##           master     #137   +/-   ##
=======================================
  Coverage   83.56%   83.56%           
=======================================
  Files           8        8           
  Lines         779      779           
=======================================
  Hits          651      651           
  Misses        128      128           

Flag	Coverage Δ
unittests	83.56% <ø> (ø)

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