Create and initialise request handler threads

Add a suicidal initialising thread `RequestInitialiser(const void *)`
that creates access-control structures, and spawns the producer
(running `RequestHandler(const void *)` and consumer
(`RequestServicer(const void *)`) threads.

The request queue is populated and emptied via a "producer-consumer"
style system. This system is run on a series of threads in a
self-contained translation unit.