Bug in Cmd2HelpFormatter and ArgparseCompleter when metavar is a tuple

[tleonhardt]

The Cmd2HelpFormatter class has a bug which causes a crash in the following circumstances:

• nargs is an int and > 1
• metavar is a tuple

Tested with cmd2 1.2.0 but verified the bug exists in the current version as well.

In my case, the crash occurs on line 780 in the current code with the _format_args method.

[tleonhardt]

Specifying metavar as a tuple only really seems to make sense if nargs is an integer greater than 1.

But perhaps the simplest solution is to remove our custom help formatting for this except when nargs is a range? (as you suggested)

[kmvanbrunt]

A metavar tuple also crashes ArgparseCompleter when creating a CompletionItem table. I will fix this in the same PR.