add doc

* Add new_doc to develop branch

* Add pics of Anakin tutorial

* Update anakin_tutorial.md

* Delete anakin_fm_en.png

* Delete contri1.JPG

* Delete contri2.JPG

* Update build_and_install_lib_cn.rst

* Update compile_paddle_lib_cn.md

* Update compile_paddle_lib_en.md

* Update install_doc.rst

* Update install_doc.rst

* expose rank_loss python api

* Update index_en.rst

* Update index_en.rst

* Update index_en.rst

* fix build doc

* add some description about Python ABI

* remove block api

* remove clone_variable

* hide block inner apis

* update

* fix tests

* Design doc of fixed-point quantization.
* Update fixed point quantization desigin doc.
* Fix doc format.
* Update the backward part.
* Fix the grammatical.

* add_nccl2_dist_design

* update

* update by comments

This is part of big move of v2 codes to legacy sub dir.

1.PaddlePaddle是百度提供的开源深度学习框架->PaddlePaddle是百度自主研发并开源的深度学习框架
2.框架本身具有易学,去掉本身
3.在兼具性能的同时->在保证性能的同时

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