Trivial NN implementations are a dime a dozen, and this one is no different. It's just a partial work in progress; it's not a 'Show HN'; it's just a few hundred lines of toy code.
...and that's the same feedback it got on /r/rust last week.
I don't see why it's turned up here now.
(Just as a baseline, at this point, if you can't use your NN implementation to at least do a basic classifier on MNIST, its probably not worth showing people)