homing: Create Homing class from gcode

Create the Homing class in the gcode handler instead of in the
kinematic classes.  This will make it easier to pass error messages
back to the user.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/cartesian.py

@@ -31,10 +31,9 @@ class CartKinematics:
     def get_homed_position(self):
         return [s.position_endstop + s.get_homed_offset()*s.step_dist
                 for s in self.steppers]
-    def home(self, toolhead, axes):
+    def home(self, homing_state):
         # Each axis is homed independently and in order
-        homing_state = homing.Homing(toolhead, axes)
-        for axis in axes:
+        for axis in homing_state.get_axes():
             s = self.steppers[axis]
             self.limits[axis] = (s.position_min, s.position_max)
             # Determine moves
@@ -60,7 +59,6 @@ class CartKinematics:
             # Home again
             coord[axis] = r2pos
             homing_state.plan_home(list(coord), homepos, [s], s.homing_speed/2.0)
-        return homing_state
     def motor_off(self, move_time):
         self.limits = [(1.0, -1.0)] * 3
         for stepper in self.steppers: