feat(option): builtin Option uses the Nil variant

The lazily registered builtin template now declares Nil = 0 instead of None_.

App/lib/core/Gen/Class/ClassGenGeneric.vp

@@ -73,7 +73,7 @@ novirtual class ClassGenGeneric(ClassGenBase.ClassGenBase):
         if self._find_generic_template("Option") is not None: return 1
         pp: memhub.MemBuddy* = CompilerFactory.factory.PermPool
         if pp is None: return 0
-        src: str = "renum Option[T]:\n    class Some:\n        value: T\n    None_ = 0\n"
+        src: str = "renum Option[T]:\n    class Some:\n        value: T\n    Nil = 0\n"
         tree: ast.AST* = ast.parse_ex(src, pp, pp)
         if tree is None or tree.children is None: return 0
         cd: ast.ClassDef* = None