Issue Description:

You might consider adding a function named drop(at:) to Array, ArraySlice, etc.

Note: I'd use remove(at:), but the array I'm working with is a let constant.

func drop(at index: Int) -> ArraySlice<Element> {
  precondition(indices.contains(index), "Index out of range")
  return self[..<index] + self[(index+1)...]
}

It returns a slice of the original array without the element at the specified index.

let numbers = [1, 2, 3, 4, 5]
print(numbers.drop(at: 2))
// Prints "[1, 2, 4, 5]"

See "Swift Array instance method drop(at: Int)" for more discussion.

Note: Maybe dropSubrange(_:) should also be added. This way, every "remove" instance method for removing elements from an array, for which it makes sense, has a corresponding "drop" instance method for excluding elements from an array, for when you're working with an array that's a let constant or an array that you don't want to modify.