* rewrite all code examples, test=document_fix

* refine arguments, test=document_fix

* fix desc format error, test=document_fix

* capitalize the first letter, test=document_fix

* refine api desc, test=document_fix

* fix wrong COPY-FROM label in Model docs, test=document_fix

* refine returns, test=document_fix

* refine returns, test=document_fix

* add a blank line in code block, test=document_fix