Keras-like API Merge and Wrappers (#2263)
Keras-like API Merge and Wrappers (#2263)

* merge

* update

* timedistributed

* bidirectional

* update

* update

* update bidirectional

* style

* update merge

* refine and add ser test

* refine timedistributed

* fix

* fix merge

* createmerge

* python merge ut

* meet review

* add doc

* fix style

* update

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