Add support for ARD about gpytorch HOT 3 CLOSED

class Kernel(Module):
    def __init__(self, has_lengthscale=True, ard_num_dims=None, log_lengthscale_bounds=(-10000, 10000)):
        self.ard_num_dims = ard_num_dims
        if has_lengthscale:
            lengthscale_num_dims = 1 if ard_num_dims is None else ard_num_dims
            self.register_parameter('log_lengthscale', torch.nn.Parameter(torch.Tensor(1, 1, ard_num_dims)),
                                    bounds=log_lengthscale_bounds)

    @property
    def lengthscale(self):
        if 'log_lengthscale' in self.named_parameters().keys():
            return self.log_lengthscale.exp()
        else:
            return None


# ...


class RBFKernel(Kernel):
    def __init__(self, **kwargs):
        kwargs['has_lengthscale'] = True
        super(RBFKernel, self).__init__(**kwargs)
        # ...