Initial IR change

Fixed unittests for WITH_GPU=OFF and WITH_DISTRIBUTE=OFF build

fix dead link in high_level_api.md

better installation doc

fix mac build

* Added beam search API to fluid/contrib

* Change as review comments

* API.spec change

* Doc updated

fix _clone_variable in optimizer.py

Delete overview.rst from api index

hide more apis

Update build script

 move contrib/inference to paddle/fluid/inference/api

fix set-e exit when checking api