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

serial.c

@@ -49,19 +49,19 @@ volatile uint8_t tx_buffer_tail = 0;
   }
 #endif
 
-static void set_baud_rate(long baud) {
-  uint16_t UBRR0_value = ((F_CPU / 16 + baud / 2) / baud - 1);
+void serial_init()
+{
+  // Set baud rate
+  #if BAUD_RATE < 57600
+    uint16_t UBRR0_value = ((F_CPU / (8L * BAUD_RATE)) - 1)/2 ;
+    UCSR0A &= ~(1 << U2X0); // baud doubler off  - Only needed on Uno XXX
+  #else
+    uint16_t UBRR0_value = ((F_CPU / (4L * BAUD_RATE)) - 1)/2;
+    UCSR0A |= (1 << U2X0);  // baud doubler on for high baud rates, i.e. 115200
+  #endif
   UBRR0H = UBRR0_value >> 8;
   UBRR0L = UBRR0_value;
-}
-
-void serial_init(long baud)
-{
-  set_baud_rate(baud);
-  
-  /* baud doubler off  - Only needed on Uno XXX */
-  UCSR0A &= ~(1 << U2X0);
-          
+            
   // enable rx and tx
   UCSR0B |= 1<<RXEN0;
   UCSR0B |= 1<<TXEN0;
@@ -159,11 +159,7 @@ ISR(USART_RX_vect)
     case CMD_STATUS_REPORT: sys.execute |= EXEC_STATUS_REPORT; break; // Set as true
     case CMD_CYCLE_START:   sys.execute |= EXEC_CYCLE_START; break; // Set as true
     case CMD_FEED_HOLD:     sys.execute |= EXEC_FEED_HOLD; break; // Set as true
-    case CMD_RESET:
-      // Immediately force stepper and spindle subsystem idle at an interrupt level.
-      mc_alarm();
-      sys.execute |= EXEC_RESET; // Set as true
-      break;
+    case CMD_RESET:         mc_reset(); break; // Call motion control reset routine.
     default: // Write character to buffer    
       next_head = rx_buffer_head + 1;
       if (next_head == RX_BUFFER_SIZE) { next_head = 0; }