HeaderMap's TryFrom<HashMap> is not generic over the hashing algorithm used

[Qqwy]

HeaderMap<T> implements TryFrom<&'a HashMap<K, T>>. However, this only covers hashmaps created with the default S = RandomState hashing algorithm / state.
If you've gathered some headers from elsewhere (in my case: in a Python library with PyO3) and you want to turn those into a HeaderMap for use in a HTTP client, there is no need to use a HashDoS-resistant hashing function, so being able to use a hashmap with a different hashing function would be great.

As far as I can tell, there is no reason why the current implementation could not work for other hashmaps. The only thing that needs to change is exposing S parameter as well in the trait implementation bounds.

[seanmonstar]

That makes sense, want to submit a PR?

[Qqwy]

Yes, will do!