Add Python Reader Op (CPP side)

Add design doc of Python data feeding

create about_us.rst

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

Fix and enhance beam_search_op and beam_searc_decode_op

Fix dist train broadcasting bug

增加【关于我们】文案

* change return_numpy[PE] default value

* Remove convert to numpy in unit test

enable dynamic load mklml lib on fluid

Checkpoint M2: lookup table checkpoint

Fix async update failed

Update api.rst (merge to develop)

* elementwise_add with bcast: Brian's implementation by Brian added, with default bcasts

* elementwise_add with bcast: GetExpectedKernelType added to elementwise_op

* elementwise_add with bcast: use_mkldnn attribute added

* elementwise_add with bcast: changes after review and some formatting

* elementwise_add with bcast: changes after style check

* elementwise_add with bcast: changes after style check cont.

* elementwise_add with bcast: MKLDNN unittests added

* elementwise_add with bcast: original unittests with use_mkldnn flag

* elementwise_add with bcast: handling of MKLDNN format corrected

* elementwise_add with bcast: setting MKLDNN format turned into lambda

* elementwise_add with bcast: MKDNN format setting turned into separate function

* elementwise_add with bcast: condition for choosing MKLDNN simplified

* elementwise_add with bcast: fix for MKLDNN format set incorrectly in bcasts

* elementwise_add with bcast: changes in unittests for broadcasts

* elementwise_add with bcast: fixes in unittests regarding dimensions

* elementwise_add with bcast: bring back correct format setting in mklml grad path

* elementwise_add with bcast: fixed compilation error

fix sparse paraexe dist train