Add --argument-passthrough option

[MadLittleMods]

Fixes https://github.com/kimmobrunfeldt/concurrently/issues/33

Add --argument-passthrough option

Barebones example

concurrently --argument-passthrough "echo foo" "echo bar" -- --some-arg
->
echo foo --some-arg
echo bar --some-arg

With npm scripts

concurrently --argument-passthrough "npm run foo" "npm run bar" -- -- --some-arg
-> 
npm run foo -- --some-arg
npm run bar -- --some-arg

Todo

• Figure out best way to test this (suggestions welcome)

[MadLittleMods]

@kimmobrunfeldt Friendly ping for thoughts and timeline

[gustavohenke]

Don't you prefer to skip --arguments-passthrough?
So as soon as you have -- bla, the arguments are passed through 😉

However, if you have examples of programs that work similarly, we could review the need of such option.

[MadLittleMods]

@gustavohenke Having no option seems fine. Any thoughts on how to test?

[gustavohenke]

Codebase changed significantly and this PR has been inactive for a good time.
I'm closing it; feel free to open an issue to discuss the approach before starting over.