This allows tokio-signal to build with `-Z minimal-versions` - see
https://github.com/rust-lang/cargo/issues/5657#issuecomment-401110172
for more details.
Earlier versions depend on log 0.3.1, which itself depends on libc
0.1, which doesn't build on any post-1.0 version of rust.
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.
Daniel Wagner-Hall