TODO

My exposure to Java tainted me. I need to do a little bit more thinking about
the relationship between TaskS and ThreadS. My task class is based on being
notified that the timer has expired and then pushes an privately-defined user
event onto the queue. I like the benefits of being able to avoid lot of the
synchronization issues. A Task_thread class could attach itself to the user
event as a listener and be notified using a Condition...

- Add RAII objects for surface readers/writers/helpers, etc.
- Use iterator-based interface in get/set_colours (Surface).
- Disable operator= for wrappers (inherit from class noncopyable).
- Finer-grained Timer classes.
- Turn runtime_error into sdl_error;
- Condition: Turn runtime_error thrown by wait_timeout into a timeout_error.