Collect variadic arguments

Mark the final parameter name: ...Type to collect surplus arguments into a fresh array. A call may supply none. The fixed part of the signature still has normal arity.

Variadic functions are called directly. They cannot be stored as function values, passed by name, or fed an existing array with spread syntax.

fn sum(values: ...int) -> int {
  let mut total = 0
  for value in values { total += value }
  total
}

fn main() {
  println(sum())
  println(sum(1, 2, 3, 4))
}