first milestone

vector.scala

// all elements are `Int`, `N` is the size of the vector
trait Vector[N] {
  def map(f: Int => Int): Vector[N]
  def pad(x: Int): Vector[x + N]
  def concat[M](v: Vector[M]): Vector[M + N]
  def splitAt(i: Int): (Vector[i + 1], Vector[N - i - 1])
  def slice(i: Int, j: Int): Vector[j - i + 1]
  def dot(v: Vector[N]): Int
  def size: Int
}