Fix diode check limits, allow for two-mode continuity limit

D1 has changed to a 5V1 zener and is loading the circuit a little bit. Adjusted voltage based on tested value on prototype. This value may differ on production units so expect this to possibly change.

include/probe.h

@@ -16,6 +16,9 @@ void probe_mode_switch(uint8_t mode);
 
 void probe_measure();
 
+void probe_set_thresh(uint8_t set);
+uint8_t probe_get_thresh();
+
 
 
 #endif /* _INC_PROBE_H */

include/userio.h

@@ -34,6 +34,9 @@ int16_t userio_get_btn();
 
 uint8_t userio_get_set1_limit();
 
+int16_t userio_get_btn_held();
+void userio_set_btn_override();
+
 
 
 #endif /* _INC_USERIO_H */