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Some error codes are renamed
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This mostly is cleanup, with fewer alternative methods and more standard syntax, avoiding the use of the namespace all the time. Validators are simpler and are added through `->check()`. Defaults are automatic, and can be specified with a final arg to the options. Expected arguments and required arguments are now accessed through a pointer to option. Option now can be checked as a bool to see if the argument was passed. Errors have better organisation.