Re-factored system states and alarm management. Serial baud support greater than 57600.

- Refactored system states to be more clear and concise. Alarm locks
processes when position is unknown to indicate to user something has
gone wrong.

- Changed mc_alarm to mc_reset, which now manages the system reset
function. Centralizes it.

- Renamed '$X' kill homing lock to kill alarm lock.

- Created an alarm error reporting method to clear up what is an alarm:
message vs a status error: message. For GUIs mainly. Alarm codes are
negative. Status codes are positive.

- Serial baud support upto 115200. Previous baudrate calc was unstable
for 57600 and above.

- Alarm state locks out all g-code blocks, including startup scripts,
but allows user to access settings and internal commands. For example,
to disable hard limits, if they are problematic.

- Hard limits do not respond in an alarm state.

- Fixed a problem with the hard limit interrupt during the homing
cycle. The interrupt register is still active during the homing cycle
and still signal the interrupt to trigger when re-enabled. Instead,
just disabled the register.

- Homing rate adjusted. All axes move at homing seek rate, regardless
of how many axes move at the same time. This is unlike how the stepper
module does it as a point to point rate.

- New config.h settings to disable the homing rate adjustment and the
force homing upon powerup.

- Reduced the number of startup lines back down to 2 from 3. This
discourages users from placing motion block in there, which can be very
dangerous.

- Startup blocks now run only after an alarm-free reset or after a
homing cycle. Does not run when $X kill is called. For satefy reasons

motion_control.h

@@ -43,7 +43,7 @@ void mc_dwell(float seconds);
 // Perform homing cycle to locate machine zero. Requires limit switches.
 void mc_go_home();
 
-// Kills all motion and sets system alarm
-void mc_alarm();
+// Performs system reset. If in motion state, kills all motion and sets system alarm.
+void mc_reset();
 
 #endif