Inserts a new key and value into a glib.HashTable
If the key already exists in the glib.HashTable its current value is replaced with the new value. If you supplied a value_destroy_func when creating the glib.HashTable, the old value is freed using that function. If you supplied a key_destroy_func when creating the glib.HashTable, the passed key is freed using that function.
Starting from GLib 2.40, this function returns a boolean value to indicate whether the newly added value was already in the hash table or not.