signal: Implement the wake-up part of the new signal handling

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.

src/lib.rs

@@ -25,6 +25,8 @@
 #[macro_use]
 extern crate futures;
 extern crate tokio_core;
+#[macro_use]
+extern crate lazy_static;
 
 use futures::Future;
 use futures::stream::Stream;