Finds all point-value pairs in a
KdMap with points within a
given range, where the range is specified as a set of lower and upper
bounds.
Points are not returned in any particular order.
Worst case time complexity:
O(n) for n data points and a range
that spans all the points.
TODO: Maybe use known bounds on entire tree structure to be able to
automatically count whole portions of tree as being within given
range.