Implement ascontiguousarray() or contiguous() method

[Rikorose]

See https://docs.scipy.org/doc/numpy/reference/generated/numpy.ascontiguousarray.html or https://pytorch.org/docs/stable/tensors.html#torch.Tensor.contiguous

A method like this is e.g. needed when passing &ndarray.as_slice() to an external api.

[andrei-papou]

@LukeMathWalker could you please take a look at the PR? Thanks.