Update pip version

Update  pip install paddle-serving-app==0.2.0

原命令：pip install paddle-serving-server-gpu==0.4.0.trt # GPU with CUDA10.1+TensorRT

新命令：pip install paddle-serving-server-gpu==0.4.0.100 # GPU with CUDA10.1+TensorRT

fix grpc impl, sync with brpc

fix gbk in win

Fix Readme 0.4

Update README.md

fix win doc and move requirements

Docs fix

Fix invalid variable 'path'

[WIP] 0.4 index page readme

Pull lastest codes

revert Merge Pull Request #689, the support encryption model

fix doc/COMPILE.md doc/DOCKER_IMAGES.md by Thomas Young