Inserts a key/value mapping into the hash table.
Note that insert doesn't remove the old entry from the table - the behaviour is like an association list, the most-recently-inserted mapping for a key in the table. The reason for this is to keep insert as efficient as possible. If you need to update a mapping, then we provide update.
The insert function takes an element and a list and inserts the element into the list at the last position or equal to the next element. In particular, if the list is sorted before the call, the result will also be sorted. It is a special case of insertBy, which allows the programmer to supply their own comparison function.
The non-overloaded version of insert.