* refine name descrip. test=document_preview

* fix doc of pool2d pool3d. test=develop,test=document_preview

* fix doc according to reviews. test=develop,test=document_preview

* fix doc according to reviews from XiaoguangHu01 and raindrop2sea. test=develop,test=document_preview

* refine doc: pool2d/3d, adaptive_pool2d/3d, grid_sampler, kldiv_loss,
spectral_norm, temporal_shift. test=document_preview

* refine doc: exponential_decay, inverse_time_decay, natural_exp_decay. test=document_preview

* refine doc. test=document_preview

* refine doc for learning_rate_scheduler. test=document_preview

* refine OP. test=document_preview

* fix kldiv_loss. test=document_preview

* fix spectral_norm formula. test=document_preview