* Implement homing cycle in stepper.c
* Implement limit switch support in stepper.c (use port-triggered interrupts?)
* How to implement st_set_pace? Consider synchronizing when pace is changed
* Eliminate need for circle_x and circle_y in step_arc_along…
* Use timer interrupts to drive steppers
* Tool table
* Tool length offsets
* Tool change M6
* Coolant control
* Path Control Modes
* Spindle speed support