add basic constraint demo
towards GPU joint (non-contact) constraint solving. The ConstraintDemo shows that CPU performance is very good, so not much performance win is to be expected.
Merge branch 'master' of https://github.com/erwincoumans/bullet3
add b3FixedConstraint, with less memory footprint than b3Generic6DofConstraint, and easier to port to OpenCL.
remove the 'obsolete' part of b3Generic6DofConstraint and b3Point2PointConstraint
work towards GPU joint solver (non-contact constraints), not working yet.
work towards GPU joint solver (non-contact constraints), not working yet.