* switching from a naive algorithm with multiple O(n) operation plus one at worst of O(log(n)) operations to a more optimal one.
* the topk algorithm returns the top k elements in a content, with a strict O(n) (n being the number of characters) complexity.
* this topk algorithm is inspired from the space saver algorithm implemented in redis.
* this system keep tracks of the number of occurences of each words, and their location in the topk array. Each new parsed word can be either inserted in the array, or swaped with another element.
* updating the unit tests, with a first set of basic tests