Exercise 10.2. Write a function called cumsum that takes a list of numbers and returns the cumulative sum; that is, a new list where the ith element is the sum of the first i + 1 elements from the original list. For example:
>>> t = [1, 2, 3]
>>> cumsum(t)
[1, 3, 6]
Exercise 10.3. Write a function called middle that takes a list and returns a new list that contains all but the first and last elements. For example:
>>> t = [1, 2, 3, 4]
>>> middle(t)
[2, 3]
