Homing and limit updates. Minor bug fixes.

- Updated new homing cycle to error out when a pull-off motion detects
the limit is still active.

- Created a limits_get_state() function to centralize it. It reports
state as a bit-wise booleans according to axis numbering.

- Updated the print uint8 functions. Generalized it to allow both base2
and base10 printouts, while allowing base2 prints with N_AXIS digits
for limit state status reports. Doing this saved about 100bytes of
flash as well.

- Applied CoreXY status reporting bug fix by @phd0. Thanks!

grbl/system.c

@@ -252,8 +252,10 @@ float system_convert_axis_steps_to_mpos(int32_t *steps, uint8_t idx)
   #ifdef COREXY
     if (idx==A_MOTOR) { 
       pos = 0.5*((steps[A_MOTOR] + steps[B_MOTOR])/settings.steps_per_mm[idx]);
-    } else { // (idx==B_MOTOR)
+    } else if (idx==B_MOTOR) {
       pos = 0.5*((steps[A_MOTOR] - steps[B_MOTOR])/settings.steps_per_mm[idx]);
+    } else {
+      pos = steps[idx]/settings.steps_per_mm[idx];
     }
   #else
     pos = steps[idx]/settings.steps_per_mm[idx];