support batch_size for decoder (#246)
support batch_size for decoder (#246)


mli/gluon-tutorials-zh,d2l-ai/d2l-zh,d2l-ai/d2l-zh,mli/gluon-tutorials-zh,d2l-ai/d2l-zh,mli/gluon-tutorials-zh,mli/gluon-tutorials-zh