Add a "pwd" utility to userland.

It's implemented as a separate process. How cute is that.
Tasks now have a current working directory. Spawned tasks inherit their
parent task's working directory.
Currently everyone just uses "/" as there's no way to chdir().

Kernel/init.cpp

@@ -150,7 +150,7 @@ static void init_stage2()
     }
 #endif
 
-    auto* shTask = Task::create("/bin/sh", (uid_t)100, (gid_t)100);
+    auto* shTask = Task::create("/bin/sh", (uid_t)100, (gid_t)100, (pid_t)0);
 
     banner();