`hashmap_put` and `hashmap_remove` may need to return old values

[xuning0]

Only in this way can it be convenient to release the old value on heap.

[strayLuo]

void* hashmap_remove_and_get_value(struct HashmapS* const m, 
    const char* const key,
    const unsigned len)
{
    void* element = HASHMAP_NULL;

    unsigned int i;
    unsigned int curr;

    /* Find key */
    curr = hashmap_hash_helper_int_helper(m, key, len);
    /* Linear probing, if necessary */
    for (i = 0; i < HASHMAP_MAX_CHAIN_LENGTH; i++) {
        if (m->data[curr].in_use) {
            if (hashmap_match_helper(&m->data[curr], key, len)) {
                element = m->data[curr].data;
                //free(m->data[curr].key); //the key should be freed
                memset(&m->data[curr], 0, sizeof(struct HashmapElementS));

                /* Reduce the size */
                m->size--;
                break;
            }
        }

        curr = (curr + 1) % m->table_size;
    }
    return element;
}

[strayLuo]

你看看这个是否符合需求，但是可能违背了此项目的设计。key由外界申请，并由外界释放。
Look at this to see if it meets the requirements, but it may go against the design of this repository. key is malloced by user and freed by user.