Small speed improvement int trim by using stack (and DFS) instead of queue (and BFS) for remove and collapse, finally fix the unknown escape '\*' error

stdlib/ast_transformation.krak

@@ -1,6 +1,7 @@
 import symbol:*
 import tree:*
 import vector:*
+import queue:*
 import stack:*
 import map:*
 import util:*