* Update avg_pool signature to be consistent with ngraph AvgPool.

- Change parameters order and use more appropriate paramter names.
- Add docstring.

* Single file with test for pooling operations.

- Add test for avg_pool for 2D case.

* Code refactoring.

- Rename parameters to be more verbose.
- Change function return type, to enable general usage.

* Add UT for ceil, ceiling and abs.

* Update docstrings and type annotations.

* Add UT for broadcast operation.

* Add UT for concat operation.

- Minor change: add optional node name function parameter.

* Code formatting.

* UT for constant and convert operations.

- Move broadcast test to test_basic.py file.

* Update function signature.

- Update to be consistent with nGraph object API.

* Review fix.

- Update type annotations.
- Update docstring.
- Change local variables names to be consistent.

* Refactoring - put some commonly used functions into util.py.

* Update convolution operation signature.

- Add docstring
- Update to be consistent with respective nGraph object API.
- Formatting in UT.

* Fix import statements under py27.

* Correct quotation marks.

* Revert changes: use AxisSet as a return type.

* Review fix.

- Update parameter names to be consistent with respective parameters of nGraph object constructors.

* Review fix

- Set seed for random number generation to be repeatable.
- Use numpy.allclose.

* Change serialize routine

* Change serialize routine call for onnx

* Run clang-format on constant.cpp

* Update function type annotation.