Implement listening for signals based on signalfd().

tests/0-signal.d

@@ -0,0 +1,37 @@
+/++ dub.sdl:
+	name "test"
+	dependency "eventcore" path=".."
++/
+module test;
+
+import eventcore.core;
+import std.stdio : writefln;
+import core.stdc.signal;
+import core.sys.posix.signal : SIGRTMIN;
+import core.time : msecs;
+
+bool s_done;
+
+void main()
+{
+	auto id = eventDriver.signals.listen(SIGRTMIN+1, (id, status, sig) {
+		assert(!s_done);
+		assert(status == SignalStatus.ok);
+		assert(sig == () @trusted { return SIGRTMIN+1; } ());
+		s_done = true;
+		eventDriver.core.exit();
+	});
+
+	auto tm = eventDriver.timers.create();
+	eventDriver.timers.set(tm, 500.msecs);
+	eventDriver.timers.wait(tm, (tm) {
+		() @trusted { raise(SIGRTMIN+1); } ();
+	});
+
+	ExitReason er;
+	do er = eventDriver.core.processEvents();
+	while (er == ExitReason.idle);
+	//assert(er == ExitReason.outOfWaiters); // FIXME: see above
+	assert(s_done);
+	s_done = false;
+}