Added samples and prefixes to variables

ziffers/classes/items.py

@@ -479,6 +479,13 @@ class Variable(Event):
     name: str
 
 
+@dataclass(kw_only=True)
+class Sample(Event):
+    """Class for samples"""
+
+    name: str
+
+
 @dataclass(kw_only=True)
 class VariableList(Item):
     """Class for using variables"""