Initial v0.8 ALPHA commit. Features multi-tasking run-time command execution (feed hold, cycle start, reset, status query). Extensive re-structuring of code for future features.

- ALPHA status. - Multitasking ability with run-time command executions
for real-time control and feedback. - Decelerating feed hold and resume
during operation. - System abort/reset, which immediately kills all
movement and re-initializes grbl. - Re-structured grbl to easily allow
for new features: Status reporting, jogging, backlash compensation. (To
be completed in the following releases.) - Resized TX/RX serial buffers
(32/128 bytes) - Increased planner buffer size to 20 blocks. - Updated
documentation.

stepper.h

@@ -3,6 +3,7 @@
   Part of Grbl
 
   Copyright (c) 2009-2011 Simen Svale Skogsrud
+  Copyright (c) 2011 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
@@ -29,16 +30,22 @@
 #define DIRECTION_MASK ((1<<X_DIRECTION_BIT)|(1<<Y_DIRECTION_BIT)|(1<<Z_DIRECTION_BIT)) // All direction bits
 #define STEPPING_MASK (STEP_MASK | DIRECTION_MASK) // All stepping-related bits (step/direction)
 
-// Initialize and start the stepper motor subsystem
+// Initialize and setup the stepper motor subsystem
 void st_init();
 
-// Block until all buffered steps are executed
-void st_synchronize();
+// Immediately disables steppers
+void st_go_idle();
 
-// Execute the homing cycle
-void st_go_home();
+// Reset the stepper subsystem variables       
+void st_reset();
              
 // Notify the stepper subsystem to start executing the g-code program in buffer.
 void st_cycle_start();
 
+// Reinitializes the buffer after a feed hold for a resume.
+void st_cycle_reinitialize(); 
+
+// Initiates a feed hold of the running program
+void st_feed_hold();
+
 #endif