First stage in refactoring Bullet: moved Bullet Collision and Dynamics and LinearMath into src folder, and all files in Collision Detection and Dynamics have bt prefix.

Made all buildsystems to work again (jam, msvc, cmake)

lib/readme.txt

@@ -0,0 +1,13 @@
+At the moment there are no binary packages from Bullet library.
+Once this is done, 3 libraries will be placed here:
+
+bulletmath.a
+bulletcollision.a
+bulletdynamics.a
+
+The C-API will be available in the include folder.
+
+For now, there is only C++ files, see src/btBulletCollisionCommon.h and src/btBulletDynamicsCommon.h
+
+http://bullet.sf.net
+Erwin Coumans