Library with the (some of) best known strategies for the K-nht smallest element in an array/sequence.
Might come handy for other algorithms that require median finding such as a KD-tree and others. The only strategy so far is the implementation of [Quickselect with random pivot](https://en.wikipedia.org/wiki/Quickselect) which is O(n) on average. Sorting and finding the middle element would be O(n logn) usually. It changes the input array so you should clone it before if this is an issue.
