Issue #725

* make sure we don't get insidious perf bugs due to doule op::Results
* fix graph_partition tests

* make matmulbias callback aware that addition is commutative

* make sure deserializer doesn't add op::Result twice

* Added new ctor for bn which supports Inference
- added mkldnn emitter code for bn inference
* Added test case for bn inference
- added support for layout propogation for bn inference
* added sanity checks for gamma, beta, mean, variance shape in bn
* added serializer support for bn inference

* general dot for gpu

* Current cudnn implementations use only
a single dimension for the ngraph tensor data (width).
In this case the tensor format should be set to

CUDNN_TENSOR_NCHW

so that adjacent memory accesses are coalesced (stride=1 for width).

* * Added some kernel emitter helpers that are reused often.
* Renamed EmitElementwise -> emit_elementwise to match emit<T>.
* op::Sum now handles trivial case of dim(input_tensor) = dim(output_tensor)
  by performing a memcpy as no axes are reduced.

*   Added general case for Nd descriptors which is used when the tensor
  has more than 4 dimensions. Currently a naive reduce is performed,
  in the future a coordinate transformation could be performed to
  improve the memory layout for the reduction.

* Switched to codegen::CodeWriter::block_begin/end.
It appears that CodeWriter::block_begin/end is not frequently used for emitters (in cpu and gpu transformers)
because a block comment is often desired. To this end I added prefix/suffix default parameters to CodeWriter::block_begin/end
so that this functionality is captured.

* Added backprop op for relu and enabled tests.

* Remove examples from pybind wrapper
* Adding back example (basic.py)

* update nnp transformer path

Adjust CallFrame argument order to match Function

* rename directories to be consistent
* rename reference namespace to match directory

* Remove unnecessary Optional type annotations.

* Implement PR review changes

* cleanup neon integration documentation

* topolotical-sort based node clustering

* cmake builds

* Argon manager renamed to NNP along with placement

* nnp dir cmake changes

* tests pass

* more renames

* somemore renames

* reslove redefination

* revert to ARGON_API

* more PR comments and remove nnp-fusion tests as redundant

* update path

* fix format

* global tracing

* fix compiler errors

* nan/inf validation

* 0644 on mkldnn_utils.cpp

* address Bob's feedback

* 0755 -> 0644

* remove format changes to python dir

* add visualize option to nbench

* check for dot, amend help msg

* fix a segfault while printing shapes for multi-output ops

Updates to docs

* add python dir to check-code-format and re-run apply-code-format on it

* 0644 -> 0755

* File renaming missed in git add earlier

* More doc validation for neon install

* Typo on sphinx syntax for ordered list

* Missed a delete

* More clarity on optional steps WRT virtualenv and opt dirs

* Rendering subbullets as bullets for clarity and fix typo

* New docbuild graphic now working

* Framework intg guide updated with ngraph-neon doc improvements