Make num_hashes mean the num_hashes since the last ID

Before this change, num_hashes meant the number of hashes since
the last ID, minus any hashing done on the event data. It made
no difference for Tick events, but logged Transaction events with
one less hash than actually occurred.

src/logger.rs

@@ -61,6 +61,7 @@ impl<T: Serialize + Clone + Debug> Logger<T> {
     pub fn log_event(&mut self, event: Event<T>) -> Result<(), (Entry<T>, ExitReason)> {
         if let Some(sig) = get_signature(&event) {
             self.last_id = extend_and_hash(&self.last_id, &sig);
+            self.num_hashes += 1;
         }
         let entry = Entry {
             id: self.last_id,