add ForwardHandler and use it where appropriate
Fix some macros to work outside APrinter namespace.
add IndexElemList and use it in IndexElemTuple implementation
WrapCallback: allow the method and member to be relative to different classes, as long as static_cast works between them
ForwardHandler: don't rely on return type deduction
MotionPlanner: move bit count specifications int a separate type
AxisStepper: move some parameters into a type
MotionPlanner: remove unneeded handler