Add watchdog to turn off relays in a hang

Prevents a hang from keeping the heater or pump relays always on, which
could cause the thermal fuses to burn or the pump to empty the deposit
and then burn as well.

barista/barista.ino

@@ -3,6 +3,7 @@
 
 #include "ntc.h"
 #include "pinout.h"
+#include <avr/wdt.h>
 
 enum logic {
 	ON = 1,
@@ -326,6 +327,7 @@ void do_output(const struct state *st)
 
 void setup()
 {
+	wdt_disable();
 	Serial.begin(9600);
 	Serial.println("Booting");
 
@@ -342,6 +344,7 @@ void setup()
 	relay(PIN_PUMP, OFF);
 
 	Serial.println("Ready");
+	wdt_enable(WDTO_250MS);
 }
 
 void loop()
@@ -351,4 +354,5 @@ void loop()
 	do_output(&g_st);
 
 	delay(5);
+	wdt_reset();
 }