fix cross op doc for API2.0

Add new operator api: paddle.histc(input, bins=100, min=0, max=0)

Add index sample op cn doc

* test=develop, add_tril_op

* test=develop, polish_addmm_op

* test=develop, add_triu_op

* test=develop, polish tril and triu

* add cn doc of unbind API

Add the Chinese doc for the api of equal, linspace, matmul

* Implement the chinese documentation of inverse.

* Add the documentation of error type.

* Remove the example of static graph.

add the doc of chinese document randint

* test=develop, add addmm doc

* add addmm doc

* test=develop, add addmm doc

* add cn doc of trace API

* add cn doc of diag_embed API

* add bmm arange api_doc test=develop

* Add randperm cn doc, test=develop, test=document_preview

* add doc for kron op, test=document_preview

* add support for integer types, test=document_preview

* add cross, roll, index_select, nonzero api_cn

* test=document, add cross,index_select,nonzero,roll cn doc

* test=document, bug fix for syntax error

* add paddle.sin, sqrt, tanh, atan cn doc to fluid docs

* Add Chinese document of API: randn

paddle.add doc for elementwise_add operator 
paddle.div doc for elementwise_div operator 

add the the mul and pow api to the fluid tensor doc 

* add cn doc for dot and logsumexp