add Vehicles/Hinge2Vehicle demo, based on the ForkLift demo, using btHinge2Constraint with rigid body wheels

change btHinge2Constraint to derive from new btGeneric6DofSpring2Constraint

examples/SimpleOpenGL3/main.cpp

@@ -0,0 +1,57 @@
+#include "OpenGLWindow/SimpleOpenGL3App.h"
+#include "Bullet3Common/b3Vector3.h"
+#include "Bullet3Common/b3CommandLineArgs.h"
+#include "assert.h"
+#include <stdio.h>
+#include "OpenGLWindow/OpenGLInclude.h"
+
+char* gVideoFileName = 0;
+char* gPngFileName = 0;
+
+int main(int argc, char* argv[])
+{
+    b3CommandLineArgs myArgs(argc,argv);
+
+
+	SimpleOpenGL3App* app = new SimpleOpenGL3App("SimpleOpenGL3App",1024,768);
+	app->m_instancingRenderer->setCameraDistance(13);
+	app->m_instancingRenderer->setCameraPitch(0);
+	app->m_instancingRenderer->setCameraTargetPosition(b3MakeVector3(0,0,0));
+
+    assert(glGetError()==GL_NO_ERROR);
+
+    myArgs.GetCmdLineArgument("mp4_file",gVideoFileName);
+    if (gVideoFileName)
+        app->dumpFramesToVideo(gVideoFileName);
+
+    myArgs.GetCmdLineArgument("png_file",gPngFileName);
+    char fileName[1024];
+
+	do
+	{
+	    static int frameCount = 0;
+		frameCount++;
+		if (gPngFileName)
+        {
+            printf("gPngFileName=%s\n",gPngFileName);
+
+            sprintf(fileName,"%s%d.png",gPngFileName,frameCount++);
+            app->dumpNextFrameToPng(fileName);
+        }
+
+		assert(glGetError()==GL_NO_ERROR);
+		app->m_instancingRenderer->init();
+		app->m_instancingRenderer->updateCamera();
+
+		app->drawGrid();
+		char bla[1024];
+		sprintf(bla,"Simple test frame %d", frameCount);
+
+		app->drawText(bla,10,10);
+		app->swapBuffer();
+	} while (!app->m_window->requestedExit());
+
+
+	delete app;
+	return 0;
+}