internal/outcome: rename from app

This is less ambiguous, and more accurately describes the purpose of the package.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/outcome/shim-signal.h

@@ -0,0 +1,3 @@
+#include <signal.h>
+
+void hakurei_shim_setup_cont_signal(pid_t ppid, int fd);