Building CampaignHawk: Clustering with Leaflet Markercluster (Part 17)

Continuing the discussion from Building CampaignHawk: Spacial Analysis Overview (Part 16):

Part 17 goes over Leaflet and Markercluster. I spent some time looking into clustering algorithms, which were pretty complicated, but then I found Markercluster, which made the whole process almost trivially easy.