Lot of refactoring for the future. CoreXY support.

- Rudimentary CoreXY kinematics support. Didn’t test, but homing and
feed holds should work. See config.h. Please report successes and
issues as we find bugs.

- G40 (disable cutter comp) is now “supported”. Meaning that Grbl will
no longer issue an error when typically sent in g-code program header.

- Refactored coolant and spindle state setting into separate functions
for future features.

- Configuration option for fixing homing behavior when there are two
limit switches on the same axis sharing an input pin.

- Created a new “grbl.h” that will eventually be used as the main
include file for Grbl. Also will help simply uploading through the
Arduino IDE

- Separated out the alarms execution flags from the realtime (used be
called runtime) execution flag variable. Now reports exactly what
caused the alarm. Expandable for new alarms later on.

- Refactored the homing cycle to support CoreXY.

- Applied @EliteEng updates to Mega2560 support. Some pins were
reconfigured.

- Created a central step to position and vice versa function. Needed
for non-traditional cartesian machines. Should make it easier later.

- Removed the new CPU map for the Uno. No longer going to used. There
will be only one configuration to keep things uniform.

probe.c

@@ -2,7 +2,7 @@
   probe.c - code pertaining to probing methods
   Part of Grbl v0.9
 
-  Copyright (c) 2014 Sungeun K. Jeon
+  Copyright (c) 2014-2015 Sungeun K. Jeon
 
   Grbl is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -63,7 +63,7 @@ void probe_state_monitor()
     if (probe_get_state()) {
       sys.probe_state = PROBE_OFF;
       memcpy(sys.probe_position, sys.position, sizeof(float)*N_AXIS);
-      bit_true(sys.execute, EXEC_FEED_HOLD);
+      bit_true(sys.rt_exec_state, EXEC_FEED_HOLD);
     }
   }
 }