* optimize sampling

* fix comments

* len(data) only once

Merge branch 'feature/support_pytorch_demo' of github.com:ChunweiYan/VisualDL-1 into feature/support_pytorch_demo

* Add test for graph edges

* add new line

* add google protobuf

* add onnx to travis

* install protoc and move installs to tests.sh

* tune protoc

* try to install onnx

* onnx always fails on travis, try script from onnx github

* install protobuf 3.1.0 but not onnx

* in the right dir

* tune path

* should work

* put onnx_pb2 there and it should work

* what if remove onnx_pb2.py

* cp compiled onnx_pb2 to the right place

* debug

* protoc

* install protoc

* chown

* test

* added protc, should work

* typo

* does it exist?

* hmmmm

* try dropbox

* test 1

* now it should work

* done

* make tests more thorough

Fixed some compilation errors and unit test failure

* link in eigen3 library to vl_test target
* Add new "template class SimpleWriteSyncGuard<Entry<long long>>;", since build will fail on OSX
* Add template keyboard to data<T>(0).Get() (otherwise this fails on OSX)
* Fix unit test in sdk_test.cc

Tested build and unit test run on OSX and Ubuntu with no issues

Merge branch 'feature/support_pytorch_demo' of github.com:ChunweiYan/VisualDL-1 into feature/support_pytorch_demo