#5 definable float type

[Jeremy Swigart]

It's not difficult to do this myself, but in an effort to minimize future merge headaches it would be useful if there was an option in opensteer to use doubles for all the floating point types. I'm experimenting with opensteer in a large simulation environment where the coordinate system can exceed the precision that a float provides, and having the option to turn opensteer to double mode would be very useful, similar to how some physics engines allow you to use them in double precision mode by a #define and such.