New jog cancel real-time command. Parser typo fix from last push.

- Added a new jog cancel real-time command. Rather than depending on a
feed hold to cancel a jogging motion, this realtime command can be used
instead. The main advantage is if a feed hold is used, you can
accidentally hold the machine right when Grbl returns to IDLE after
completing a jog. And the GUI doesn’t have to worry about tracking this
either.

- Fixed a typo in the g-code parser edits from the last push. Was
causing the G10 set coordinate system command to not work correctly.

- Updated the documentation with the jog cancel command.

doc/log/commit_log_v1.1.txt

@@ -1,3 +1,18 @@
+----------------
+Date: 2016-09-27
+Author: Sonny Jeon
+Subject: Refactored g-code parser. Saved 60bytes flash and some ram. Edited Readme.
+
+- Freed up another 60 bytes of flash and 12-24 bytes of stack RAM by
+using the pre-allocated IJK arc offset vector that is guaranteed to be
+not in use. Only G10 and G28/30 require fetching from EEPROM and
+retaining extra data. Both commands use axis words, which rules out
+G2/3 arcs using IJK offsets existing in same block. Not ideal, but
+every byte helps.
+
+- Edited README.
+
+
 ----------------
 Date: 2016-09-27
 Author: Sonny Jeon