add links of preview tool

update paddle submodule in develop

update survey doc

 update paddle changes and add api_guides folder 

delete repeated tensor in script

delete redundant files

 copy Paddle-develop content to develop 

refine cluster train quickstart

update develop api_doc according paddle repo

Just copy the whole API folder

update book submodule in develop branch

update 0.15.0 docs in fluiddoc according to paddle repo

* update gen_doc_lib

* Update the script to make it simpler

* update submodule

* Start over

* Added basic docs
Added .travis.yml
Added scripts to build documentation on the Travis.

* Disable several deploy script commend for testing.

* fixed the deploy_docs.sh script.

* Update travis.yml

* Renamed docs to doc

* update .gitignore.

* Delete .gitignore

* Update .travis.yml

* Update .travis.yml

* Update deploy_docs.sh

* Update .travis.yml

* Develop doc (#1)

* Add paddle submodule

* Update the build script.

* Update script

* Use gen_doc_lib instead.

* Move files around

* cache external

* Update submodule

* try to cache batch 1

* add test code

* Update Paddle submodule

* Update submodule

* update script to print more

* update python path

* test

* test

* test

* clean up the code

* Update Script (#2)

* add new file

* Develop doc (#3)

* Add the rest of the submodules into the system

* Provide first symlink fit a line

* Update the rest of book to symlinks

* add models submodule

* Add link for models

* Update deploy_docs

* update to use lite 2

* Develop doc (#4)

* Include the en book

* Deploy mobile and models.

* Use external approach.