Third time's a charm! No more deceleration issues! Updated grbl version and settings. General cleanup.

- Fleshed out the original idea to completely remove the long slope at
the end of deceleration issue. This third time should absolutely
eliminate it.
- Changed the acceleration setting to kept as mm/min^2 internally,
since this was creating unneccessary additional computation in the
planner. Human readable value kept at mm/sec^2.
- Updated grbl version 0.7d and settings version to 4. NOTE: Please
check settings after update. These may have changed, but shouldn't.
- Before updating the new features (pause, e-stop, federate override,
etc), the edge branch will soon be merged with the master, barring any
immediate issues that people may have, and the edge branch will be the
testing ground for the new grbl version 0.8.

stepper.h

@@ -38,8 +38,7 @@ void st_synchronize();
 // Execute the homing cycle
 void st_go_home();
              
-// The stepper subsystem goes to sleep when it runs out of things to execute. Call this
-// to notify the subsystem that it is time to go to work.
-void st_wake_up();
+// Notify the stepper subsystem to start executing the g-code program in buffer.
+void st_cycle_start();
 
 #endif