Queue.</a></h3>
   This priority queue implementation depends on a static number of priorities
   (-20 (high) to 20 (low)) so that tuple access times can be exploited for
   quick in/out priority queue operations.  This implementation was created to
   avoid the slowness within the priority queue used by both RabbitMQ and Riak
   (https://github.com/basho/riak_core/blob/master/src/priority_queue.erl).
<h2><a name="types">Data Types</a></h2>

<h3 class="typedecl"><a name="type-pqueue">pqueue()</a></h3>
<p><t