Lazy Classifier - KNN

ML/FieldAggregates.ecl
support KDTree endless right-node propagation.
ML/Trees.ecl
modify KDTree, changes support KNN Search:
  . use variance to select split feature (more balanced tree)
  . detect leaf branches: only one instance or same value for all instances
  . avoid endless right-node propagation
  . add FullTree and Boundaries, support KNN Search
ML/Lazy.ecl
define instance-based learning (lazy) classifier (default, general).
define KNN classifier (particular).
ML/NearestNeighborsSearch.ecl
define NearestNeighborsSearch, general KNN search Algorithm (default).
define KDTreeNNSearch, particular KNN search using KDTree.
ML/Test/Explanatory/KNN_KDTree.ecl
explanatory examples for KNN-KDTree classifier.