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.

gcode.c

@@ -127,10 +127,8 @@ uint8_t gc_execute_line(char *line) {
       switch(int_value) {
         case 0: gc.motion_mode = MOTION_MODE_SEEK; break;
         case 1: gc.motion_mode = MOTION_MODE_LINEAR; break;
-#ifdef __AVR_ATmega328P__        
         case 2: gc.motion_mode = MOTION_MODE_CW_ARC; break;
         case 3: gc.motion_mode = MOTION_MODE_CCW_ARC; break;
-#endif        
         case 4: next_action = NEXT_ACTION_DWELL; break;
         case 17: select_plane(X_AXIS, Y_AXIS, Z_AXIS); break;
         case 18: select_plane(X_AXIS, Z_AXIS, Y_AXIS); break;
@@ -226,7 +224,6 @@ uint8_t gc_execute_line(char *line) {
       mc_line(target[X_AXIS], target[Y_AXIS], target[Z_AXIS], 
         (gc.inverse_feed_rate_mode) ? inverse_feed_rate : gc.feed_rate, gc.inverse_feed_rate_mode);
       break;
-#ifdef __AVR_ATmega328P__
       case MOTION_MODE_CW_ARC: case MOTION_MODE_CCW_ARC:
       if (radius_mode) {
         /* 
@@ -336,7 +333,6 @@ uint8_t gc_execute_line(char *line) {
         r, isclockwise);
         
       break;
-#endif      
     }    
   }