v2.4.0

Feedback blocks.

Thorough expansion of the feedback module.
Feedback blocks automatically handle weight coupling and skip connections.

When defining a feedback block in the network's layers, the following syntax is used:

network.feedback(
    vec![feedback::Layer::Convolution(
        1,
        activation::Activation::ReLU,
        (3, 3),
        (1, 1),
        (1, 1),
        None,
    )],
    2,
    true,
);