reimplement enum.auto() for compatibility with older python 3 versions

ast.py

@@ -1,6 +1,20 @@
 # fx-92 Scientifique Collège+ language interpreter: AST definition
 
-import aenum as enum
+import enum
+
+def auto_builder():
+    number = 0
+    def auto():
+        nonlocal number
+        number += 1
+        return number
+    return auto
+
+try:
+    enum.auto()
+except AttributeError: 
+    enum.auto = auto_builder()
+del auto_builder
 
 #---
 # Internal AST node representation