export/import_nir__Adding-Conv2D_and_AvgPool2d

[SirineArfa]

• fixes #304
• Adding support for the following torch.nn modules [Conv2d, AvgPool2d and Flatten] to _exportnir.py and _importnir.py
• Create example notebook in _examples/tutorial_snntorch_tonir.ipynb for snntorch model with layers [Conv2d, AvgPool2d,LIF, Linear,LIF] and export/import it to NIR
• Include this model's tests in _tests/testnir.py

[SirineArfa]

• The pip version of NIR is not automatically updated and is currently version 1.0.1 from Dec 25. Hence, it does not contain AvgPool2d yet.

• To try this feature you must build NIR from source:

  • git clone https://github.com/neuromorphs/NIR.git
  • cd NIR
  • pip install .