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.

report.h

@@ -2,7 +2,7 @@
   report.h - reporting and messaging methods
   Part of Grbl v0.9
 
-  Copyright (c) 2012-2014 Sungeun K. Jeon
+  Copyright (c) 2012-2015 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
@@ -54,9 +54,10 @@
 #define STATUS_GCODE_G43_DYNAMIC_AXIS_ERROR 37
 
 // Define Grbl alarm codes. Less than zero to distinguish alarm error from status error.
-#define ALARM_LIMIT_ERROR -1
-#define ALARM_ABORT_CYCLE -2
-#define ALARM_PROBE_FAIL -3
+#define ALARM_HARD_LIMIT_ERROR -1
+#define ALARM_SOFT_LIMIT_ERROR -2
+#define ALARM_ABORT_CYCLE -3
+#define ALARM_PROBE_FAIL -4
 
 // Define Grbl feedback message codes.
 #define MESSAGE_CRITICAL_EVENT 1