Buffer is a mutable data structure with two operations:

1. append an element
2. convert the buffer to an array or arrays.

• Internally it is stored as a growable sequence of arrays. It never recopies data internally during an append, but it may allocate during append.
• It is specialized for primitive types.
• It can store more elements than Int.MaxValue, however in this case toArray will throw (use toArrays).

val b = org.saddle.Buffer.empty[Int]
// b: org.saddle.Buffer[Int] = org.saddle.Buffer@5e6c0510
    b += 3
// res0: org.saddle.Buffer[Int] = org.saddle.Buffer@5e6c0510
    b.toArray
// res1: Array[Int] = Array(3)