Migrate from optparse to argparse (fixes #107)

[hartwork]

Fixes #107

[codecov]

Codecov Report

❌ Patch coverage is 84.37500% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 15.67%. Comparing base (18fe331) to head (4e3334a).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
gprof2dot.py	84.37%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #108       +/-   ##
===========================================
- Coverage   85.70%   15.67%   -70.03%     
===========================================
  Files           1        1               
  Lines        2449     2449               
===========================================
- Hits         2099      384     -1715     
- Misses        350     2065     +1715     

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[jrfonseca]

Thanks.

[LucaBH]

Bug left, see #111