Command-line argument parsing and validation for Go.
Args.go recognizes three types of arguments: parameters, options and flags. Flags are standalone arguments of the form "--flag" or "-f"; options are the same format, but immediately followed by a (single) value. A parameter is simply a single argument, without a leading hyphen.
Flags and options will be consumed wherever they are found in the arguments. Parameters are consumed in the order they are included on the command line.
The Args library works on an array of command-line arguments (usually
os.Args[1:]). Each operation returns the argument requested, as well as the
array with that argument removed, so that it can be passed to additional Arg
calls.