* raise error when cannot get shape in reshape

* fix pylint

* AlterOpLayout with tvm.target

* fix test

* fix restore layout in AlterOpLayout

* lint test case

* allow missing FCorrectLayout

* misunderstood OpMap[], fix

* rename FInferLayout -> FCorrectLayout

* correct stupid IDE

* update submodule tvm

* Issue fix for tiny yolo

There was an issue in maxpool frontend for tiny-yolo. It is fixed in PR. 
https://github.com/dmlc/nnvm/issues/431

* updated review comment, python 3 compatabilty

* Update darknet.py

* Updated review comment

* Update TVM to latest

* remove darknet from testing due to cffi

* declare type for optional tshape

* add doc

* move code to another place

* [DOCS] add a solution to installation error

* Fix the command for updating submodules

* fix same var used in single op

* revert to older version

* initial NHWC layout support

* remove layout param from softmax

* more nhwc support

* fix typo

* add nhwc layout test

* fix lint

* update tvm

* update for c++ topi

* fix lint

* update tvm

The below compilation warning is fixed.

In file included from /mnt/D_DRIVE/work/nnvm_8_feb/dmlc-core/include/dmlc/any.h:16:0,
                 from include/nnvm/./base.h:11,
                 from include/nnvm/graph.h:15,
                 from src/compiler/fold_scale_axis.cc:6:
src/compiler/fold_scale_axis.cc: In function ‘nnvm::Graph nnvm::compiler::FoldScaleAxis(nnvm::Graph)’:
src/compiler/fold_scale_axis.cc:155:39: warning: enum constant in boolean context [-Wint-in-bool-context]
     CHECK(kind == kPassTroughFirst || kMulConsumer);
                                       ^
/mnt/D_DRIVE/work/nnvm_8_feb/dmlc-core/include/dmlc/./logging.h:110:9: note: in definition of macro ‘CHECK’
   if (!(x))