Update to accept generic object types (instead of the specific CPoint type)

Christian,

I ran into your Obj-C DBScan implementation.  I forked it and updated it so the scanner and cluster classes accepted a generic object type (id) instead of the CPoint specific implementation.

This allows the use of CLLocationCoordinate2D and CCLoction objects in iOS and OS X.

I also fixed several Xcode 5 compiler warnings. I thought you might be interested.

Also, I would like to use DBScan in one or more of my projects.  Can you update your readme with license details or contact me directly with permission-to-use details?

Thanks,
-jjamminjim