* Fix truncated normal.

* Fix.

* Make nce support more distribution.

* Fix API.spec.

* Fix python API.

* Fix.
test=develop

* Fix API.spec
test=develop

* Fix sampler.

* Fix order of arguments in python API.
test=develop

* NCE add selectedrows support

* NCE update weighted sampling

* fix bugs in nce_op, and assign_value_op optimized

* fix bugs in nce_op, revert assign_value_op

* nce_op optimize

* nce_op optimize

* nce_op optimize

* add selectedRows test later

test=develop

* add selectedRows supported

* add selectedRows supported

test=develop

* add selectedRows supported

* add nce selectedRows supported, test=develop

* add nce selectedRows supported

* add nce selectedRows supported, test=develop

* fix height in nce, test=develop

* add ut

* add ut, test=develop

* make AutoGrownIndex inline
test=develop

* fix tinny error, test=develop

Fix Mac unittest bug

add some activation api examples.

clean inference include files

fix interpolate_op incompatible. test=develop

Fea/jit/rnn

test=develop

Add python3.6 and python3.7 support to production generated Dockerfile

Windows/online

Upgrade pybind11 to v2.2.4 to support Python3.7

test=develop

test=develop

test=develop

test=develop

test=develop

* Transpose-Flatten-Concat fusion operator.
* Add unit testing and fix bug.

fix compile

test=develop

fix Mac unittest error on reading pined memory flag

*  fix mkdir conflict

*  fix load/save lookup tables

 test=develop

* add lookup_table_utils

* fix load optimize vars on pserver

* delete lookup table utils

* fix save and load lookup tables

* fix load optimizer var

* fix load optimizer var, test=develop

* fix python 3 style, test=develop

* move lookup_table_utils to contrib utils

refine prelu api doc