Feature Req: Making the channel argument optional

[torridgristle]

If the channel argument is set to None, keep the filter kernel with only one channel and then in the forward pass use PyTorch's .expand() function to match the input's channel count. I'm uncertain of the performance impact so only having this as an optional behavior seems safest.

This helps with testing before finalizing a design since you don't have to change the channel argument each time the channel count changes.