convert AST_Seq from binary tree to array (#1460)

- rename `AST_Seq` to `AST_Sequence`
- raise default sequences_limit from 200 to 800

lib/transform.js

@@ -174,9 +174,8 @@ TreeTransformer.prototype = new TreeWalker;
         self.args = do_list(self.args, tw);
     });
 
-    _(AST_Seq, function(self, tw){
-        self.car = self.car.transform(tw);
-        self.cdr = self.cdr.transform(tw);
+    _(AST_Sequence, function(self, tw){
+        self.expressions = do_list(self.expressions, tw);
     });
 
     _(AST_Dot, function(self, tw){