Move trainer to contrib

fix table grad send sync_mode

* generic cmake

* Update generic.cmake

* add nccl2 dist api

* update apispec

* update

* update api spec

* add guide

* "fix doc"

* Update windows_inference.md

Looks like there is a little problem in markdown format writing of head lines

Remove kwargs in softshrink

fix links in readme

fix roi_perspective_transform_op.cc unused variable caused error on Mac

fix img_conv_group doc

Remove kwargs in elementwise layers and scale layer

disable memopt test

 remove kwargs of some activation api

* add ShareLoDs

* refine

* add Is EmptyVarName

* refine Sharedlod

remove the kwargs of elu,relu6,pow,stanh,hard_sigmoid and swish

Enhance eager delete and sparse Adam

Revert "Merge pull request #13431 from chengduoZH/refine_lod"

* Fix truncated normal.

* Fix.

Fix unstable selected_rows_functor_test.cu

* wip

* clean up

* should fix running with memopt

* add ut

* mark lr schedule op role

* hide lr_schedule_guard

* use op_role_var instead of ufind

* unify dist test name

* wip for py3 support

* fix var deref

* fix python3 mem_opt order

* remove comments

fix conflicts