Write a function named collapse that accepts an array of integers as a parameter and returns
a new array where each pair of integers from the original array has been replaced by the sum of that pair.
For example, if an array called arr stores [7, 2, 8, 9, 4, 13, 7, 1, 9, 10], then the call
of collapse(arr) should return a new array containing [9, 17, 17, 8, 19].
The first pair from the original array is collapsed into 9 (7 + 2), the second pair is collapsed into 17 (8 + 9), and so on.
If the array stores an odd number of elements, the last element is not collapsed.
For example, if the array had been [1, 2, 3, 4, 5], then the call would return [3, 7, 5].
Your function should not change the array that is passed as a parameter.
