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.

grbl/protocol.c

@@ -575,10 +575,16 @@ static void protocol_exec_rt_suspend()
             // Execute slow pull-out parking retract motion. Parking requires homing enabled, the
             // current location not exceeding the parking target location, and laser mode disabled.
             // NOTE: State is will remain DOOR, until the de-energizing and retract is complete.
+            #ifdef ENABLE_PARKING_OVERRIDE_CONTROL
+            if ((bit_istrue(settings.flags,BITFLAG_HOMING_ENABLE)) &&
+                            (parking_target[PARKING_AXIS] < PARKING_TARGET) &&
+                            bit_isfalse(settings.flags,BITFLAG_LASER_MODE) &&
+                            !sys.override_ctrl) {
+            #else
             if ((bit_istrue(settings.flags,BITFLAG_HOMING_ENABLE)) &&
                             (parking_target[PARKING_AXIS] < PARKING_TARGET) &&
                             bit_isfalse(settings.flags,BITFLAG_LASER_MODE)) {
-
+            #endif
               // Retract spindle by pullout distance. Ensure retraction motion moves away from
               // the workpiece and waypoint motion doesn't exceed the parking target location.
               if (parking_target[PARKING_AXIS] < retract_waypoint) {
@@ -642,7 +648,12 @@ static void protocol_exec_rt_suspend()
             #ifdef PARKING_ENABLE
               // Execute fast restore motion to the pull-out position. Parking requires homing enabled.
               // NOTE: State is will remain DOOR, until the de-energizing and retract is complete.
+              #ifdef ENABLE_PARKING_OVERRIDE_CONTROL
+              if (((settings.flags & (BITFLAG_HOMING_ENABLE|BITFLAG_LASER_MODE)) == BITFLAG_HOMING_ENABLE) &&
+                  !sys.override_ctrl) {
+              #else
               if ((settings.flags & (BITFLAG_HOMING_ENABLE|BITFLAG_LASER_MODE)) == BITFLAG_HOMING_ENABLE) {
+              #endif
                 // Check to ensure the motion doesn't move below pull-out position.
                 if (parking_target[PARKING_AXIS] <= PARKING_TARGET) {
                   parking_target[PARKING_AXIS] = retract_waypoint;
@@ -676,7 +687,12 @@ static void protocol_exec_rt_suspend()
 
             #ifdef PARKING_ENABLE
               // Execute slow plunge motion from pull-out position to resume position.
+              #ifdef ENABLE_PARKING_OVERRIDE_CONTROL
+              if (((settings.flags & (BITFLAG_HOMING_ENABLE|BITFLAG_LASER_MODE)) == BITFLAG_HOMING_ENABLE) &&
+                  !sys.override_ctrl) {
+              #else
               if ((settings.flags & (BITFLAG_HOMING_ENABLE|BITFLAG_LASER_MODE)) == BITFLAG_HOMING_ENABLE) {
+              #endif
                 // Block if safety door re-opened during prior restore actions.
                 if (bit_isfalse(sys.suspend,SUSPEND_RESTART_RETRACT)) {
                   // Regardless if the retract parking motion was a valid/safe motion or not, the