* Add DataFeeder

A v2 API like data feeder for book demos.
We can feed data directly from reader.

* Fix CI

* Add an unittest for while/rnn op forward

* Add unittest for raw while op backward

* Fix CI

* Add hinge loss op

* Update hinge-loss equation for proper latex

* fix grpc compile warn

* update

* -Wnon-virtual-dtor -> -Wno-non-virtual-dtor

Also, change the `labels` to `label` for api consistency

* Fix Proformance problem of enforce

* Fix missing `;` in code

* Fix CI

* add back print_operators_doc

* fix style check

* fix style check

* fix compile on cudnn7

* update

* update

* make silent

* Adding log loss operator

* Removing comments

* batch norm support matrix input

* update gpu code

* format code

* Make 'scale_op' supporting int and int64

* refine .cu file

* Add Python wrap of conv2d_transpose and its unittest

* Follow comments

* Fix format

1. Remove checking for num_neg_samples.
2. Fix dims of Output(Cost) and Input(Bias).
3. Renamed num_sampled_classes to num_neg_samples.
4. Add TODO for add more distribution sampler.
5. Init grad_data of bias by zero.
6. Refine comments.
7. Register a kernel for type double.

* WIP send recv op

* WIP send recv

* put grpc impl in details

* put grpc impl in details

* update wip

* update proto

* update proto

* update proto

* clean cmake

* wip on op implementations

* wip on op implementations

* compile ok adding ut

* wip unitest

* add extern cares for linking

* wip add ut

* working version send recv

* revert optimizer.py

* update test cmake

* add libtool to dockerfile

* update cmake dependency

* update cmake depends

* update cmake grpc depends

* fix cmake dependency

* fix compile error

* fix compile

* follow comments

* update

* update copyfrom

* Fix the latex comment syntax in sgd_op.cc

* Change \textunderscore to \_