NEW: rootCommandParser CE

Added a rootCommandParser to provide the opportunity to manually parse and invoke a root command (since the rootCommand is auto-executing).

open FSharp.SystemCommandLine
open System.CommandLine.Parsing

let app (words: string array, separator: string option) =
    let separator = separator |> Option.defaultValue ", "
    System.String.Join(separator, words) |> printfn "Result: %s"
    0
    
[<EntryPoint>]
let main argv = 
    let words = Input.Option(["--word"; "-w"], Array.empty, "A list of words to be appended")
    let separator = Input.OptionMaybe(["--separator"; "-s"], "A character that will separate the joined words.")

    let parser = 
        rootCommandParser {
            description "Appends words together"
            inputs (words, separator)
            setHandler app
        }

    parser.Parse(argv).Invoke()