Fix error in score comparison

- Previously, the code compared each score against the previous score only
- Changed this so that the new score calculated is compared against the best score
- In most cases, the previous score and the best score would probably be the same,
	but it's better to be more robust
Rename to clara_kmeans_exercise.py
Merge branch 'play' of https://github.com/csojinb/gadsdc1 into csojinb-play

Conflicts:
	18-clustering/clara_kmeans_exercise.py
Merge branch 'csojinb-play'