(*) Use pointer to PxPoint. Measured ~3 times speed improvement for > 100 hits.
  (*) Relocate the vector of PxPoint pointers in cluster_params
  (*) Adding MergeAlgNew ... will develop merging algorithm here: algorithm only concerns 2 clusters at a time. The old version has some complexity due to handling all clusters in an event, which is more like module's job.

Kazu