Extracted tests and updated Pytorch version

[thomasahle]

This follows https://github.com/HazyResearch/structured-nets/issues/7 in which we discussed updating the code to use PyTorch's complex tensors.

The pull request also extracts all tests into a tests/ directory, so it's easy to run unit tests. All 12 of which pass.

Other than there there are no changes, except auto formatting which my tools unfortunately don't allow me not to use.