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.

nuts_bolts.c

@@ -3,6 +3,7 @@
   Part of Grbl
 
   Copyright (c) 2009-2011 Simen Svale Skogsrud
+  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
@@ -37,10 +38,9 @@ int read_double(char *line, uint8_t *char_counter, double *double_ptr)
   return(true);
 }
 
-
 // Delays variable defined milliseconds. Compiler compatibility fix for _delay_ms(),
 // which only accepts constants in future compiler releases.
 void delay_ms(uint16_t ms) 
 {
   while ( ms-- ) { _delay_ms(1); }
-}
+}