input: Write a python function to find the maximum subarray sum.
  assert maxSubArraySum([1, -2, 3, 4, -5, 6]) == 8
  assert maxSubArraySum([-1, -2, -3, -4]) == 0
  assert maxSubArraySum([5, -1, 2, -3, 7, -2, 3]) == 12
output: def maxSubArraySum(arr):
      max_current = max_global = 0
  
      for num in arr:
          max_current = max(num, max_current + num)
          if max_current > max_global:
              max_global = max_current
  
      return max_global