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.

settings.h

@@ -26,11 +26,11 @@
 #include <math.h>
 #include <inttypes.h>
 
-#define GRBL_VERSION "0.7c"
+#define GRBL_VERSION "0.7d"
 
 // Version of the EEPROM data. Will be used to migrate existing data from older versions of Grbl
 // when firmware is upgraded. Always stored in byte 0 of eeprom
-#define SETTINGS_VERSION 3
+#define SETTINGS_VERSION 4
 
 // Current global settings (persisted in EEPROM from byte 1 onwards)
 typedef struct {