* Enhance upsample operator to adapt onnx opset version 9 for nnvm compiler

* Add upsample test case for newer opset in nnvm

* re-trigger the CI

* [Frontend][TF] Fix Placeholder issue

* Add test cases

* [Relay][Frontend] TF Round Sign Pow Exp Reverse

* fix ci

* fix comments

* Update pretty_printer.cc

* Update pretty_printer.cc

* Implement nn.bias_add compute in C++

* Address comments

* Remove unnecessary check

* save

* fix

* Update fuse_ops.cc

return false mean retry in the future, and in the case of error, it should be report ASAP, not retry.

* fix APP_STL for latest android ndk

* add vulkan sdk for tutorial

* add android tutorial

* fix of invalid input layer name

* update relay build opt_level 1 -> 3

* Add Relay compiler pass tutorial docs

* Add Python API hook wrapping step

* Incorporate feedback

* More doc iteration

* Mooooore iteration

* Rewrite `runtime.md` in rst

Due to the previous changes the frontend resnet example failed to build.  So this patch 

1) fixes it 
2) adds ~~a local `run_tests.sh` to remedy non-existence of MXNet CI (used in python build example)~~ the example build to CI with random weights and a flag for pretrained resnet weights

Please review: @tqchen @nhynes @kazimuth

* fix bug of device_index

* cpplint

* nose

* Update test_pass_annotation.py

* fix name of testcase

* delete comment

* [Relay] C++ GraphRuntimeCodegen

* [Test] Deprecate Python2

* [Python3] Add Py2 check

* Update _pyversion.py

* [Python3] Update test

* Add gradient operator tutorial docs

* Incorporate Steven's and Ziheng's feedback

* Remove TODO about `collapse_sum_like`

* Add more examples

* [NIT] fix common error message

Extremely minor issue, but this is one of the most common error messages people see...

* Update type_solver.cc

trigger CI

Signed-off-by: Ce Gao <gaoce@caicloud.io>

Thanks @alexeyr . This is now merged.