Add conformances to support Swift ArgumentParser?

[JetForMe]

The Swift ArgumentParser library makes it easy to parse command-line arguments. I feel like it should be possible to directly provide a Path argument:

struct
Calculate : ParsableCommand
{
	@Option(name: .shortAndLong, help: "Path to input word list, one per line")
	var inputWordList: Path = Path.cwd/"wordlist.txt"
}

extension
Path : ExpressibleByArgument
{
	public init?(argument: String) {
		if let p = Path(argument)
		{
			self = p
		}
		else
		{
			return nil
		}
	}
}

but the ExpressibleByArgument conformance seems clunky to me.

[JetForMe]

Oh oops never mind, ExpressibleByArgument is part of ArgumentParser, not Swift.

[mxcl]

In general: happy to accept PRs for additions that make sense