Resolve "Operation Traversing"

Implemented the traverse method for an operation. This creates a generator with start point in the given operation. The traverse method uses BFS. Closes #11 (closed)

b_asic/abstract_operation.py

@@ -4,7 +4,7 @@ TODO: More info.
 """
 
 from abc import abstractmethod
-from typing import List, Dict, Optional, Any
+from typing import List, Set, Dict, Optional, Any
 from numbers import Number
 
 from b_asic.port import InputPort, OutputPort
@@ -107,14 +107,8 @@ class AbstractOperation(Operation, AbstractGraphComponent):
 
 		return neighbours
 
-	def traverse(self) -> List[Operation]:
-		"""Traverse the the operation tree and return operation where type matches.
-		If the type is None then return the entire tree.
-
-		Keyword arguments:
-		type_ -- the operation type to search for (default None)
-		"""
-
+	def traverse(self) -> Set[Operation]:
+		"""Traverse the operation tree and return a generator with start point in the operation."""
 		return breadth_first_search(self)
 
 	# TODO: More stuff.