ADD: distance measure enum, changed distance to double type

src/mhtree/DistanceMeasure.java

+package mhtree;
+
+public enum DistanceMeasure {
+    NEAREST_HULL_OBJECT,
+    FURTHEST_HULL_OBJECT,
+    SUM_OF_DISTANCES_TO_HULL_OBJECTS,
+    MEDOID
+}

src/mhtree/ObjectToNodeDistanceRank.java

@@ -6,7 +6,7 @@ public class ObjectToNodeDistanceRank implements Comparable<ObjectToNodeDistance
 
     private final Node node;
     private final LocalAbstractObject object;
-    private final float distance;
+    private final double distance;
 
     public ObjectToNodeDistanceRank(Node node, LocalAbstractObject object) {
         this.node = node;
@@ -15,7 +15,7 @@ public class ObjectToNodeDistanceRank implements Comparable<ObjectToNodeDistance
     }
 
     public int compareTo(ObjectToNodeDistanceRank rank) {
-        return Float.compare(distance, rank.node.getDistance(object));
+        return Double.compare(distance, rank.node.getDistance(object));
     }
 
     public Node getNode() {