Fix #133 - force deep sleep if battery reaches 10%

src/PowerFSM.h

@@ -13,6 +13,7 @@
 #define EVENT_BLUETOOTH_PAIR 7
 #define EVENT_NODEDB_UPDATED 8     // NodeDB has a big enough change that we think you should turn on the screen
 #define EVENT_CONTACT_FROM_PHONE 9 // the phone just talked to us over bluetooth
+#define EVENT_LOW_BATTERY 10 // Battery is critically low, go to sleep
 
 extern Fsm powerFSM;