Function ritual_common::utils::add_to_multihash

pub fn add_to_multihash<K, T, V, S>(
    hash: &mut HashMap<K, V, S>, 
    key: K, 
    value: T
) where
    K: Eq + Hash + Clone,
    V: Default + Extend<T>,
    S: BuildHasher, 

Creates and empty collection at hash[key] if there isn't one already. Adds value to hash[key] collection.