Fix invalid trait implementations

[Dzejkop]

Fixes invalid trait implementations like

#[derive(Clone)]
pub struct Proof<H>(pub Vec<Branch<H::Hash>>)
where
    H: Hasher;

where Clone would only be implemented if the Hasher was Clone. Not if the hash type was clone

[0xForerunner]

It sorta sucks having to manually implement things like Debug. I had a think about a better way to accomplish this though and couldn't come up with anything. No way to tell derive to ignore the generic type.

You could probably remove the Hasher generic and implement the methods that require that through a trait, but that solution brings up a bunch of other problems. This will have to do :p

[0xForerunner]

This crate seems to solve the problem. Do you think it's worth the dependency?

[0xForerunner]

Nice! This looks pretty sweet!