* add name attribute to code-block, test=document_fix

* remove redundant labels, test=document_fix

* remove redundant labels (from upstream), test=document_fix

* more COPY-FROM (try multiple code example), test=document_fix

* empty commit, try to trigger PR-CI-build

* fix some `Examples:` format issues

* fix some ci errors

* use yapf to format all python file

* yapf exclude two unittests file for they rely on writing and reading file, and format will break them

* disable diff_py_file because too many diff files cause command following failed

* add random varaiable transformations API for paddle's distribution package

* add TransformedDistribution API for paddle's probability distribution package

* add random variable transformation unitests for static graph

* replace math.prod which not support python3.7 with functools.reduce

* add Independent and TransformedDistribution distribution

* add unittests for constraint

* fix typo and AffineTransform sample code error

* add mean,variance,rsample abstract method for Distribution