Let's suppose that the distance of a word can be calculated by summing the differences between its letters, having assigned the letters of the alphabet to integers (a = 1, b = 2, ... z = 26). For example, if

 word = 'hello'

then the total distance would be

 abs(8–5) + abs(5–12) + abs(12–12) + abs(12–15) = 3 + 7 + 0 + 3 = 13.

Let's also make this case insensitive (i.e., 'A' = 'a'). Write a function to return the distance for any word or set of words. See the test suite for examples.