Duplicate Points can be inserted

[pfw]

I've been looking into quads for some spatial indexing I need to do and I think it looks like it will do the job very nicely.

One thing I've noticed is that a point can be inserted more than once, eg. .insert(Point(1,2)) and .insert(Point(1,2)). It shows up with a recursion error when it is inserted more than 'capacity' times. I'm assuming that is expected that a point should only be inserted once but wanted to confirm before making any changes for a fix.