Program stop support (M0,M1*,M2,M30*), proper position retainment upon reset, misc minor updates.

- Program stop support (M0,M1*,M2,M30*). *Optional stop to be done.
*Pallet shuttle not supported.

- Work position is set equal to machine position upon reset, as
according to NIST RS274-NGC guidelines. G92 is disabled.

- Renamed mc_set_current_position() to mc_set_coordinate_offset().

- Fixed bug in plan_synchronize(). Would exit right before last step is
finished and caused issues with program stops. Now fixed.

- Spindle now stops upon a run-time abort command.

- Updated readme and misc upkeeping.

serial.c

@@ -3,7 +3,7 @@
   Part of Grbl
 
   Copyright (c) 2009-2011 Simen Svale Skogsrud
-  Copyright (c) 2011 Sungeun K. Jeon
+  Copyright (c) 2011-2012 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
@@ -27,6 +27,7 @@
 #include "serial.h"
 #include "config.h"
 #include "stepper.h"
+#include "spindle_control.h"
 #include "nuts_bolts.h"
 #include "protocol.h"
 
@@ -127,9 +128,10 @@ ISR(USART_RX_vect)
       case CMD_CYCLE_START:   sys.execute |= EXEC_CYCLE_START; break; // Set as true
       case CMD_FEED_HOLD:     sys.execute |= EXEC_FEED_HOLD; break; // Set as true
       case CMD_RESET: 
-        // Immediately force stepper subsystem idle at an interrupt level.
+        // Immediately force stepper and spindle subsystem idle at an interrupt level.
         if (!(sys.execute & EXEC_RESET)) { // Force stop only first time.
           st_go_idle();  
+          spindle_stop();
         }
         sys.execute |= EXEC_RESET; // Set as true
         break;