LibCore: Rewrite CArgsParser

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).