motionPlanner now deals only with OutputEvents (no Events). However, AxisStepper.getStepOutputEventSequence is a dummy function
work towards #57 - stepper driver objects (like A4988) are owned by the AxisSteppers and not a part of the ioDrivers tuple
Event class removed (#57), but remnants from event.h still present
Removed event.h as per #57
Updated changes from #57 to work with machines/generic/cartesian.h
Remove commented-out code
Update travis CI tests to do both debug & release builds