title: python sklearn KDTree with haversine distance
body: <p>I try to create a KD tree of WGS84 coordinates and find neighbors within a certain radius</p>
  
  <pre><code>from sklearn.neighbors.dist_metrics import DistanceMetric
  from sklearn.neighbors.kd_tree import KDTree    
  T = KDTree([[47.8665, 8.90123]], metric=DistanceMetric.get_metric('haversine'))
  </code></pre>
  
  <p>But get the following error:</p>
  
  <pre><code>ValueError: metric HaversineDistance is not valid for KDTree
  </code></pre>
  
  <p>How can I use haversine distance in a KD-Tree?</p>