Parser building functions.

[kmvanbrunt]

All built-in commands now use a function to create their argument parser.
This simplifies the process for overriding cmd2's default parser class.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.50%. Comparing base (acb824b) to head (101ac31).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1458      +/-   ##
==========================================
- Coverage   98.50%   98.50%   -0.01%     
==========================================
  Files          20       20              
  Lines        5566     5605      +39     
==========================================
+ Hits         5483     5521      +38     
- Misses         83       84       +1     

Flag	Coverage Δ
unittests	98.50% <100.00%> (-0.01%)	⬇️

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[tleonhardt]

Everything here looks good to me.

Would it be feasible to move most of the parser building logic to a separate file? If so would it be desirable?

My thought is that cmd2.py is a pretty large file. If it is possible to move a good chunk of related logic to a separate file, that might be a good thing. Given that many if not most of the parser builder functions are class methods, I suspect this might be impossible or painful. But it's worth a thought.

[tleonhardt]

LGTM