New configuration options.

- New configuration option at compile-time:
 - Force alarm upon power-up or hard reset. When homing is enabled,
this is already the default behavior. This simply forces this all of
the time.
 - GUI reporting mode. Removes most human-readable strings that GUIs
don’t need. This saves nearly 2KB in flash space that can be used for
other features.
 - Hard limit force state check: In the hard limit pin change ISR, Grbl
by default sets the hard limit alarm upon any pin change to guarantee
the alarm is set. If this option is set, it’ll check the state within
the ISR, but can’t guarantee the pin will be read correctly if the
switch is bouncing. This option makes hard limit behavior a little less
annoying if you have a good buffered switch circuit that removes
bouncing and electronic noise.

- Software debounce bug fix. It was reading the pin incorrectly for the
setting.

- Re-factored some of the ‘$’ settings code.

grbl/config.h

@@ -106,8 +106,8 @@
 // this feature. Since the two switches are sharing a single pin, there is no way for Grbl to tell
 // which one is enabled. This option only effects homing, where if a limit is engaged, Grbl will 
 // alarm out and force the user to manually disengage the limit switch. Otherwise, if you have one
-// limit switch for each axis, don't enable this option. By keeping it disabled, you can homing while
-// on the limit switch and not have to move the machine off of it.
+// limit switch for each axis, don't enable this option. By keeping it disabled, you can perform a
+// homing cycle while on the limit switch and not have to move the machine off of it.
 // #define LIMITS_TWO_SWITCHES_ON_AXES
 
 // Allows GRBL to track and report gcode line numbers.  Enabling this means that the planning buffer
@@ -161,9 +161,22 @@
 // with little to no benefit during normal operation.
 // #define REPORT_INPUT_PIN_STATES // Default disabled. Uncomment to enable.
 
+// When Grbl powers-cycles or is hard reset with the Arduino reset button, Grbl boots up with no ALARM
+// by default. This is to make it as simple as possible for new users to start using Grbl. When homing
+// is enabled and a user has installed limit switches, Grbl will boot up in an ALARM state to indicate 
+// Grbl doesn't know its position and to force the user to home before proceeding. This option forces
+// Grbl to always initialize into an ALARM state regardless of homing or not. This option is more for
+// OEMs and LinuxCNC users that would like this power-cycle behavior.
+// #define FORCE_INITIALIZATION_ALARM // Default disabled. Uncomment to enable.
+
 // ---------------------------------------------------------------------------------------
 // ADVANCED CONFIGURATION OPTIONS:
 
+// Enables minimal reporting feedback mode for GUIs, where human-readable strings are not as important.
+// This saves nearly 2KB of flash space and may allow enough space to install other/future features.
+// NOTE: This feature is new and experimental. Make sure the GUI you are using supports this mode.
+#define REPORT_GUI_MODE // Default disabled. Uncomment to enable.
+
 // The temporal resolution of the acceleration management subsystem. A higher number gives smoother
 // acceleration, particularly noticeable on machines that run at very high feedrates, but may negatively
 // impact performance. The correct value for this parameter is machine dependent, so it's advised to
@@ -180,8 +193,10 @@
 // step smoothing. See stepper.c for more details on the AMASS system works.
 #define ADAPTIVE_MULTI_AXIS_STEP_SMOOTHING  // Default enabled. Comment to disable.
 
-// Sets the maximum step rate allowed to be written as a Grbl setting. This value is strictly limited
-// by the CPU speed and will change if something other than an AVR running at 16MHz is used.
+// Sets the maximum step rate allowed to be written as a Grbl setting. This option enables an error 
+// check in the settings module to prevent settings values that will exceed this limitation. The maximum
+// step rate is strictly limited by the CPU speed and will change if something other than an AVR running
+// at 16MHz is used.
 // NOTE: For now disabled, will enable if flash space permits.
 // #define MAX_STEP_RATE_HZ 30000 // Hz
 
@@ -318,6 +333,17 @@
 // work well and are cheap to find) and wire in a low-pass circuit into each limit pin.
 // #define ENABLE_SOFTWARE_DEBOUNCE // Default disabled. Uncomment to enable.
 
+// Force Grbl to check the state of the hard limit switches when the processor detects a pin
+// change inside the hard limit ISR routine. By default, Grbl will trigger the hard limits
+// alarm upon any pin change, since bouncing switches can cause a state check like this to 
+// misread the pin. When hard limits are triggers, this should be 100% reliable, which is the
+// reason that this option is disabled by default. Only if your system/electronics can guarantee
+// the pins don't bounce, we recommend enabling this option. If so, this will help prevent
+// triggering a hard limit when the machine disengages from the switch.
+// NOTE: This option has no effect if SOFTWARE_DEBOUNCE is enabled.
+// #define HARD_LIMIT_FORCE_STATE_CHECK // Default disabled. Uncomment to enable.
+
+
 // ---------------------------------------------------------------------------------------
 
 // TODO: Install compile-time option to send numeric status codes rather than strings.