New EEPROM restore functions.

- Tweaked the previous EEPROM restore implementation and added new
functionality.

- `$RST=$` restores the `$$` grbl settings back to firmware defaults,
which are set when compiled.

- `$RST=#` restores the `$#` parameters in EEPROM. At times it’s useful
to clear these and start over, rather than manually writing each entry.

-`$RST=*` wipe all of the data in EEPROM that Grbl uses and restores
them to defaults. This includes `$$` settings, `$#` parameters, `$N`
startup lines, and `$i` build info string.

NOTE: This doesn’t write zeros throughout the EEPROM. It only writes
where Grbl looks for data. For a complete wipe, please use the Arduino
IDE’s EEPROM clear example.

- Refactored the restore and wipe functions in settings.c to
accommodate the new commands.

README.md

@@ -27,8 +27,8 @@ Grbl includes full acceleration management with look ahead. That means the contr
 ***
 
 _**Master Branch:**_
-* [Grbl v0.9i Atmega328p 16mhz 115200baud with generic defaults](http://bit.ly/1EiviDk) _(2015-06-18)_
-* [Grbl v0.9i Atmega328p 16mhz 115200baud with ShapeOko2 defaults](http://bit.ly/1NYIfKl) _(2015-06-18)_
+* [Grbl v0.9i Atmega328p 16mhz 115200baud with generic defaults](http://bit.ly/1EiviDk) _(2015-06-20)_
+* [Grbl v0.9i Atmega328p 16mhz 115200baud with ShapeOko2 defaults](http://bit.ly/1NYIfKl) _(2015-06-20)_
   - **IMPORTANT INFO WHEN UPGRADING TO GRBL v0.9i:** 
   - Baudrate is now **115200** (Up from 9600). 
   - Homing cycle updated. Located based on switch trigger, rather than release point.