How to customize the ``brainpy.nn.Node`` feedforward output when it relies on the feedback inputs?

[chaoming0625]

Currently, brainpy.nn.Node initialize the feedforward connections, and feedback connections in two separate functions:

• init_ff()
• init_fb()

When implementing init_ff() function, we do not know the feedback information. However, once the feedbacks are sources to initialize the node feedforward output, we cannot have the correct initialization for this node.

I think there may be some way to change this drawback.

[chaoming0625]

#232 See the latest updates.