Add the driver task, connecting the signal handler wakeups to the
wakeups of of the streams.
It is a prototype-quality code, a lot of cleanups and similar is needed.
Register the signal handler that wakes up someone through a self-pipe.
That someone doesn't yet exist, though.
Some dependencies (nix, lazy_static) added to speed up the prototyping
process. They are likely to be dropped in some future commits.
Some features (eg. preserving the previous signal handlers) are still
missing.
Alex Crichton