* add --gen_doc to ci_build

* make gen-doc conditional to build/test step

* some fix in the git diff check

* some more trick on doc diff

* updated for input/output

* updated the contrib operator doc

* fix on missing input output descriptions

* fixed the problem of missing doc string, due to protobuf optimization

* fix

* revert last change

* moved gen_doc.py to /tools/python

* fixed typo