Change delete behavior

Use mid splits for better packing

Minor optimization

Check that the right node not already sorted before performint a
sort on it after a split.

Use float64 for Nearby distances

When Go begins supporing method type parameters then we can
genericize the distances.

Added Most functions

Add generic for dimensional numeric type.

You can now do something like RTreeGN[float32, int] where
the rectangles use float32s instead of float64

Added Clear method

Add Nearby

Reduce reinsert memory

Set flag to false