FDL shift

Get the next argument from argv

Arguments
<none>
Description
Get the next argument from argv.
Example
while { $argv != {} } {
    set arg [shift]
    switch -glob -- $arg {
        "-h"   { help } 
        "-title" {
            set title [shift]
        }
        default {
            VovError "Unknown argument '$arg'"
        }
    }
}