* update 2.0 public api in all left files

* reverse device.py all list;
fix some flake8 errors

* fix some docs test=develop;test=document_fix

* add code example test=develop;test=document_fix

* fix code example test=develop;test=document_fix

* fix code example test=develop;test=document_fix

* fix code example test=develop;test=document_fix

* test=develop, fix docker with paddle nccl problem

* test=develop, Add Variable api and refine dygraph related API

* test=develop, Add Variable api and refine dygraph related API

* test=develop, refine test for new api and error info

* test=develop, refine error info and test_layers

* test=develop, add API.spec

* test=devleop, fix to_string python2 and python3 compat error and refien doc

* test=devleop, add API spec

* test=devleop, update API spec

* test=devleop, update API spec

* test=develop, invoke ci

* test=develop, fix example code

* test=develop, update API spec

* test=develop, add compat test and fix inplace campat dict error

Fix str and bytes problem
Fix sorted problem
Fix math problem
Fix CI problem