6. Double-ended queues

6.1. igraph_dqueue_init — Initialize a double ended queue (deque).
6.2. igraph_dqueue_destroy — Destroy a double ended queue.
6.3. igraph_dqueue_empty — Decide whether the queue is empty.
6.4. igraph_dqueue_full — Check whether the queue is full.
6.5. igraph_dqueue_clear — Remove all elements from the queue.
6.6. igraph_dqueue_size — Number of elements in the queue.
6.7. igraph_dqueue_head — Head of the queue.
6.8. igraph_dqueue_back — Tail of the queue.
6.9. igraph_dqueue_pop — Remove the head.
6.10. igraph_dqueue_pop_back — Remove the tail
6.11. igraph_dqueue_push — Appends an element.