Standardize command-line argument passing across backends

[jiribenes]

Motivation

Resolves #390
Resolves #318

As far as I know, with #487 merged, there are two nice ways of running an Effekt program with arguments (please correct me if I'm wrong):

1. Run the compiler directly on a file: effekt test.effekt -- hello world 42
2. First build, then run the executable: effekt test.effekt && ./out/test hello world 42

Testing

I tested this locally with:

# 1. Run the compiler directly on a file
for BACKEND in js chez-callcc chez-monadic chez-lift llvm ml; do echo -n "$BACKEND: " && effekt --backend $BACKEND test.effekt -- hello world 42; done

# 2. First build, then run the executable
for BACKEND in js chez-callcc chez-monadic chez-lift llvm ml; do effekt --backend $BACKEND --build test.effekt && echo -n "$BACKEND: " && ./out/test hello world 42; done

on a small file test.effekt:

module test

import args

def main() = {
  println(commandLineArgs())
}

Both of those print the same output:

js: Cons(hello, Cons(world, Cons(42, Nil())))
chez-callcc: Cons(hello, Cons(world, Cons(42, Nil())))
chez-monadic: Cons(hello, Cons(world, Cons(42, Nil())))
chez-lift: Cons(hello, Cons(world, Cons(42, Nil())))
llvm: Cons(hello, Cons(world, Cons(42, Nil())))
ml: Cons(hello, Cons(world, Cons(42, Nil())))

Questions

1. How do we do this on Windows? Resolved, but untested, see below!
2. Are there any other ways of running an Effekt program that I can try out?
3. How does this interact with effekt.sh?
4. How can we test this? Should we even test this?

[marzipankaiser]

LGTM, tested some variants (effekt.sh with js, chez-callcc, sbt run).