title: Sorting in O(n*log(n)) worst case
body: <p>Is there a sort of an array that works in O(n*log(n)) worst case time complexity?</p>
  
  <p>I saw in Wikipedia that there are sorts like that, but they are <em>unstable</em>, what does that mean? Is there a way to do in low space complexity?</p>
  
  <p>Is there a <em>best</em> sorting algorithm?</p>