NNVM merge to TVM repo


Dear community, after deliberation and discussion with various contributors in the community, we have decided to merge nnvm into tvm. NNVM and TVM have always been deeply tied to each other, and the combination of two provides powerful end to end compiler solution for deep learning. The code merge will ease the feature integration, tests, and community development. It also reflects our goal – building end to end deep learning compiler stack.
The merge is going to happen in the subsequent days(possibly in one or two). The initial merge simply puts current nnvm repo under folder nnvm in tvm while preserving the commit history. We will also merge the docs and test infrastructure. We will be freezing the nnvm repo during the period. New pull requests can be redirected to tvm once the merge is finished. We are sorry for the short period of trouble during the process.
We are excited about this step and believe that will bring more exciting development to the whole community.

cross post https://github.com/dmlc/nnvm/issues/518