This is a complete reimplementation of CArgsParser with a different API.
Now, CArgsParser properly supports and distinguishes between:
* Positional arguments (required or not)
* Options
Options can be short and/or long.
The API allows you to add custom option and argument types. A few types are
pre-implemented for convenience:
* Boolean options (take no value)
* String and integer options (take a required value)
* String and integer arguments
* Vector-of-string arguments
This commit doesn't include changes for all the users of CArgsParser (see next
commit for that).
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