* add sparse embedding & load vars for 2.0

Change-Id: I36b59ed5f015189dc9d9d2e34a9357722d369f1b

* fix hdfs gloo

Change-Id: Ia84d579053720ad804183e54c9a04b4f031c79c6

* fix gloo hdfs

Change-Id: I5ab982fd483cddc10adcdef0b8aa83aca976cb9e

* move loadvar/sparse embedding from incubute to static

Change-Id: I57081d3545ad2efab78c72420d2162c0eacaf3a0

* upgrade comment string to raw string

* fix string in

* fix string with ' '

* revert update on comments

* upgrade only necessary

* fix sample code checker

* fix comments with '''

* fix bilateral bug

* add fused_bn_add_relu op

* add correlation api to contrib

Integrated Trainer of Parameter Server (API add `fluid.contrib.layers.sparse_embedding` only) (#22957)

* Integrated Trainer of Parameter Server

* add bilateral slice op

* add batch fc op, test=develop

* add batch_fc_op, test=develop

* fix untest, test=develop

* rm check_dygraph, test=develop

* fix comment, test=develop

* fix comment, test=develop

* optimize rank_attention, test=develop

* use the paddle memory pool, test=develop

* set max size, test=develop

* limit the max size, test=develop

* fix the head of cu, test=develop

* add AsDispensable, test=develop

* add tdm sampler op

* fix compile bug

* fix compile bug

* fix compile bug

* fix compile bug

* test=develop, add tdm sampler unittest

* fix tdm sampler unittest

* fix input var name bug

* update tdm sampler unittest

* fix unittest

* fix unittest

* update tdm sampler unittest

* add tdm exe run unittest

* fix infershape

* test=develop, add doc

* test=develop, fix gcc8 compile bug & unittest bug

* test=develop, fix unittest

* test=develop, fix T one & zero

* test=develop, add unittest check

* test=develop, add doc smaple code & fix dype set

* test=develop, fix dtype

* test=develop, fix compile bug

* test=develop, fix unittest

* test=develop, fix unittest

* test=develop, check py3 unittest

* test=develop,fix unittest

* test=develop, fix py3&py2 unittest diff

* test=develop, fix sample code

* test=develop, fix sample code

* test=develop, fix sample code

* test=develop, fix error message

* add tdm child op

* add partial_sum_op, test=develop

* modify the Paddle Error Message, test=develop

* modify the Paddle Error Message, test=develop

* modify the bug for python3, test=develop

* modify the ut for ci, test=develop

* mv to contrib, test=develop

* use check_variable_and_dtype, test=develop

* fix ci, test=develop

* fix conflict, test=dvelop

* add partial concat, test=develop

* fix the conflict, test=develop

* fix the error, test=develop

* rm SSE4, test=develop

* add partial_concat, test=develop

* fix the grids and blocks, test=develop

* fix the Paddle_Enforce, test=develop

* fix the doc of op, test=develop

* fix the doc, test=develop

* fix the doc of the op, test=develop

* replace -1 with None, test=develop

* add special way to add distribute vars， Update Pyramid hash op

* add shuffle batch op, test=develop, test=document_preview

* fix size_t conflict and check_output test=develop, test=document_preview

* fix bug test=develop, test=document_preview

* add unittest of shuffle_batch layer test=develop, test=document_preview

* fix py coverage and op input type, test=develop, test=document_preview

* fix py coverage, test=develop

* fix en doc, test=develop

* move to contrib test=develop

* add unique_name test=develop

* invoke shuffle_batch in contrib.layers test=develop

* move tree_conv to fluid.contrib.layers

test=develop

* update API.spec for tree_conv

test=develop

* update tree_conv api to increase unit coverage

test=develop

* Enhance fused_elementwise_activation op.
test=develop

* Move the api fused_elementwise_activation to contrib.
test=develop

* Add including files.
test=develop

* Add the support of sigmoid in fused_elementwise_activetion op.

* Update API.spec.
test=develop