Fix cmake find protobuf problem

Enable drop in average and max layer

Fix the way Paddle reference ccache program

reduce docker image size by removing /build in or docker build

update docker tag, add translate for jupyter notebook

Specify book develop branch

modify api doc catalog

Fix font issue in doc

Add Book in Docker

translate install paddle using docker to chinese

Add input data interface for inference

add l2 regularization to reduce the probability of fpe exception

Use v2 attr and pooling fix sentiment train_v2.py

Add book module dir

update authors

Add submodule for book

Fix MultiGradientMachine error

Set Protobuf 3.1 in FIND_PACKAGE

Feature/recommendation v2 api