code refactor

related to #8 (closed):

• I kept changes per commit small, so the number of commits got kind of numerous...

src/icartt/dataset.py

@@ -200,7 +200,7 @@ class KeywordComment:
         self.data.append(data)
 
     def __str__(self):
-        d = "\n".join(self.data) if not self.data is [] else "N/A" # TODO: use implicit boolean instead of "is []"
+        d = "\n".join(self.data) if self.data else "N/A"
         return self.key + ": " + d