Created by: Superjomn

Currently, OpProtoAndCheckerMaker has a AddInput which adds one input

AddInput's definition is

  void AddInput(const std::string& name, const std::string& comment)

but in RecurrentOp, it can receive an indefinite inputs, for example:

RecurrentOp(x0, x1)
RecurrentOp(x0, x1, x2, x3, x4)

It is hard to make a RecurrentOp's definition using this function.