Suggestion: make Counter generic over the hashing algorithm

[HastD]

It would be useful for Counter to be generic over the hashing algorithm, in the same way that HashMap allows alternate hashing algorithms to be specified. Currently the performance of Counter is limited by the fact that it can only use the default hashing algorithm, which is significantly slower than available alternatives in many common use-cases (albeit resistant to DoS attacks, but that's not a concern in some applications).

[coriolinus]

Feel free to make a PR. This feature is not important enough to me personally that I am likely to get to it in finite time, but I'm always happy to review code. The major concern for me is ensuring that the user experience is not adversely affected, so the new generic parameter must have a default, etc.

[chris-ha458]

I thought I could get just add

pub fn new_with_hasher<S>(hash_builder: S) -> Self 
    where 
        S: BuildHasher,
    {
        Self {
            map: HashMap::with_hasher(hash_builder),
            zero: N::zero(),
        }
    }

But it seems I would need to change all of the signatures to take the hasher S as well.

this might take a bit more time and I'll give it another go after some refactoring #36 has been done.