Added a shlex.split() wrapper to have a common way of calling it.

[kmvanbrunt]

This is pretty much a refactor that provides a common way of calling shlex.split() to ensure the same arguments are always used for consistent parsing.

I also replaced parse_quoted_string() with _get_command_arg_list(). I believe the name and documentation of this function better communicates its purpose. This function also doesn't bother calling shlex.split() on an already parsed Statement object.

@kotfu I removed a unit test called test_arglist_decorator_twice. Is that an OK change? I wasn't sure the use case of having two with_argument_list decorators on one method. Let me know if I need to put it back and make the new code work with it. It would be a trivial fix for me.

[codecov]

Codecov Report

Merging #638 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #638      +/-   ##
==========================================
+ Coverage   94.22%   94.23%   +0.01%     
==========================================
  Files          11       11              
  Lines        3014     3020       +6     
==========================================
+ Hits         2840     2846       +6     
  Misses        174      174

Impacted Files	Coverage Δ
cmd2/parsing.py	100% <100%> (ø)	⬆️
cmd2/cmd2.py	94.22% <100%> (-0.02%)	⬇️

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[tleonhardt]

See my comments

[tleonhardt]

Changes look good

[kotfu]

Now that it's merged, here's my comment on the question @kmvanbrunt asked above, i.e. what's the use case for duplicate argils decorators on a single method. It was just an application of Postel's law, which is: be conservative in what you do, be liberal in what you accept from others. I have no use case for why you would need two decorators on the method, but since it was trivial to ensure that our decorator didn't break or give unexpected behavior if someone did apply it twice, I tested for it and make sure it worked.