Reduce hasher code duplication

[mborland]

All of the files contain a million copy and pasted interfaces. Instead I think we should do this more like C.

template <typename HasherType, typename T>
auto hash(HasherType h, std::span<T> s)
{
    h.init();
    h.update(s.data(), s.size());
    const auto result = h.get_digest();
    h.destroy();
    return result;
}

Same thing with update(h, s) and so on and so forth. Discussion of something similar is going on in the Hash2 review. Thoughts @ckormanyos

[mborland]

I think this would also help reduce our exposure in #141