Move all the trender threads to being tracked by a thread handler and having a uniform stop signal.

Add a timed_get function to the circular buffer which will allow queries to the circualr buffers to time out.  This is used to allow the trender to see a stop request.

This is done as part of expanding the wrapping of the pthread... calls with C++.  Starting on a interface to better track threads.

Mostly replacing magic numbers with symbolic constants and expanding comments.

This is to help properly track lifetimes of the work queues.

Put in a wrapper around pthread_create to allow specifying an arbitrary job to run in the guise of a std::function.  This keeps the flexibility (scheduler, stack size, ...) of pthreads but gives the us the ability to call more than just a void* (*)(void*).

With these changes the work queues have been moved out of object scope for both the producer and the daqd objects.  A few small static routines that were used to start worker threads in the producer/daqd are removed.