BulletSim: subclass Bullet[World|Body|Shape|Constraint] for unmanaged
to have pointers and managed to have objects.
Initial paste of XNA code. Commented out.
BulletSim: fix line endings.
BulletSim: move over and port the interface for BulletXNA.
Copied BulletSNPlugin.BulletSimAPI to a new
BulletSPlugin.BSAPIXNA.cs and then modifyed the latter to
comply with the BSAPITemplate definition. Not totally debugged
but the code is all there for an INI variable to select either
unmanaged C++ Bullet or the C# version of Bullet.
BulletSim: move selection of the unmanaged Bullet DLL from BSPlugin
into the unmanaged Bullet interface class.
BulletSim: add parameter to have Bullet output performance statistics
every so many frames. Default to off.