Best XP Week

`xp` is a list of the experience points you earned each day. Find the maximum sum of any k CONSECUTIVE days in the list. The function receives `xp` and `k`, and returns the maximum sum.

`xp` is a list of the experience points you earned each day. Find the maximum sum of any k CONSECUTIVE days in the list. The function receives `xp` and `k`, and returns the maximum sum.