v1.1f. Parking override control. Spindle enable pin option.

[ver] v1.1f update due to tweaks to interface from new parking override
control.

[new] Parking motion override control via new `M56 P0` and `M56 P1`
command, which disables and enables the parking motion, respectively.
Requires ENABLE_PARKING_OVERRIDE_CONTROL and PARKING_ENABLE enabled in
config.h. Primarily for OEMs.

[new] `M56` appears in the $G report when enabled.

[new] Five new build info identification letters. Some were missing and
a couple are new. Updated the CSV and documentation to reflect these
new items.

[new] Spindle enable pin configuration option to alter its behavior
based on how certain lasers work. By default, Grbl treats the enable
pin separately and leaves it on when S is 0. The new option turns the
enable pin on and off with S>0 and S=0. This only is in effect when a
user enables the USE_SPINDLE_DIR_AS_ENABLE_PIN option.

[fix] M4 is now allowed to work when USE_SPINDLE_DIR_AS_ENABLE_PIN is
enabled. Previously this was blocked and was problematic for laser
folks using M4.

[fix] Properly declared system variables as extern. Not sure how that
went unnoticed or why it worked up until now but it has.

[fix] EXTREMELY RARE. When AMASS is intentionally disabled and sent a
motion command that is _one step_ in length, Grbl would not actuate the
step due to numerical round-off. Applied a fix to prevent the round-off
issue.

[fix] Added a compile-time check for AMASS settings to make sure that
the numerical round-off issue doesn’t effect it. This would only happen
if someone set AMASS max levels to zero. It does not effect AMASS with
its current defaults.

[fix] Wrapped the mc_parking_motion() function in an ifdef for porting
purposes.

[fix] Fixed an issue when in inverse time mode and G0’s would require a
F word. This was not correct.

[fix] Added a note in the defaults.h file that MAX_TRAVEL values must
be positive. Some users were setting this negative and it was causing
issues.

doc/log/commit_log_v1.1.txt

@@ -1,3 +1,20 @@
+----------------
+Date: 2017-01-14
+Author: Sonny Jeon
+Subject: Tool number bug fix. Updated documentation.
+
+- [fix] Tool numbers were not being tracked and reported correctly. Now
+shows tool number values in $G when programmed.
+
+- [fix] Added a max tool number value check to the g-code parser.
+
+- [doc] Added a new error code for invalid tool number. Updated CSV and
+interface documents.
+
+- [doc] Added a implementation note for buffer state in status reports.
+Don’t rely on this data for streaming.
+
+
 ----------------
 Date: 2017-01-03
 Author: Sonny Jeon