Userland: Add a /bin/yes program (fixes #110)

Userland/yes.cpp

@@ -0,0 +1,15 @@
+#include <stdio.h>
+
+int main(int argc, char** argv)
+{
+    if (argc > 1) {
+        for (;;) {
+            puts(argv[1]);
+        }
+    } else {
+        for (;;) {
+            puts("yes");
+        }
+    }
+    return 0;
+}