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/limits.h

@@ -26,8 +26,12 @@
 // Initialize the limits module
 void limits_init();
 
+// Disables hard limits.
 void limits_disable();
 
+// Returns limit state as a bit-wise uint8 variable.
+uint8_t limits_get_state();
+
 // Perform one portion of the homing cycle based on the input settings.
 void limits_go_home(uint8_t cycle_mask);