Update colors in Sorting table and add heapsort

1. In the "Best" you're showing O(n log(n)) as yellow but O(n) as red; O(n) should be green.
2. In "Average" and "Worst" you're showing O(n log(n)) as yellow but it's the best you can do so I think green makes more sense.
3. In "Space Complexity" you are showing both O(1) and O(log(n)) as green, O(log(n)) should be yellow.

I also added heapsort. It has the same time comp'exity as mergesort but O(1) space complexity.