Read arguments: Read and validate shell command line arguments

This class can can be used to read and validate shell command line arguments.

It can parse the values of arguments passed to a PHP script started from a command line shell to validate them according to rules defined by the current script.

It supports mandatory arguments, optional arguments, switch arguments, multiple alternatives to an option switches, and a special argument that makes show a nicely formatted help usage message.

The class extract the argument values into an array if the argument rules are validated.