rsdl_bins_2d

1.  In changing, removing, and getting a value at a location, the location is converted to a bin index and then
the bin is searched.  This does not take into account that the location plus or minus the distance tolerance MIGHT 
place the desired value in a different bin.

2.  When changing, removing and getting a value at a location, there maybe more than one value at the desired
location or within the distance tolerance.  These functions only deal with the first value found and ignore the rest.

3.  Should the default value of the search tolerance be zero?
