Switches all HAL Handle errors to be zero (#100)

As discussed, we don't really need the error checking specifically, as
we are just going to throw exceptions anyway, so this will make sure you
can check for 0 and be sure you catch any handle errors.

hal/lib/athena/AnalogInput.cpp

@@ -30,7 +30,7 @@ void* initializeAnalogInputPort(HalPortHandle port_handle, int32_t* status) {
   if (*status != 0) return nullptr;
 
   int16_t pin = getPortHandlePin(port_handle);
-  if (pin == HAL_HANDLE_INVALID_TYPE) {
+  if (pin == InvalidHandleIndex) {
     *status = PARAMETER_OUT_OF_RANGE;
     return nullptr;
   }