Added btCudaBroadphase, some early research & development work to accelerate Bullet using CUDA

Re-uses the NVidia particle demo.

Extras/CUDA/particles_kernel.cuh

@@ -0,0 +1,47 @@
+#ifndef PARTICLES_KERNEL_H
+#define PARTICLES_KERNEL_H
+
+#define BLOCKDIM 64
+#define USE_SORT 1
+
+#ifndef __DEVICE_EMULATION__
+#define USE_TEX 1
+#endif
+
+#ifdef USE_TEX
+#define FETCH(t, i) tex1Dfetch(t##Tex, i)
+#else
+#define FETCH(t, i) t[i]
+#endif
+
+#include "vector_types.h"
+typedef unsigned int uint;
+
+struct SimParams {
+    float4 colliderPos;
+    float  colliderRadius;    
+
+    float3 gravity;
+    float globalDamping;
+    float particleRadius;
+
+    uint3 gridSize;
+    uint numCells;
+    float3 worldOrigin;
+    
+    float3 cellSize;
+    float3 worldSize; 
+    uint3 m_gridSize;
+
+    uint numBodies;
+    uint maxParticlesPerCell;
+
+    float spring;
+    float damping;
+    float shear;
+    float attraction;
+    float boundaryDamping;
+  
+};
+
+#endif