Add scripts/single.sh to build individual non-multiplexed standalone commands.

Alas, you can't quite do this yet:

  make defconfig
  make
  for i in $(./toybox)
  do
    echo $i
    PREFIX=singles/ scripts/single.sh $i || break
  done

Because the OLDTOY() aliases for commands won't build without the base command.
And I can't just skip them because chown/chmod or mv/cp aren't the same thing.
diff --git a/Config.in b/Config.in
index 9bac607..5f04bd8 100644
--- a/Config.in
+++ b/Config.in
@@ -10,19 +10,13 @@
 
 config TOYBOX
 	bool
-	default n
+	default y
 	help
 	  usage: toybox [command] [arguments...]
 
 	  With no arguments, shows available commands. First argument is
 	  name of a command to run, followed by any arguments to that command.
 
-config TOYBOX_SINGLE
-	bool
-	default n
-	help
-	  Build a single toybox command standalone with no multiplexer.
-
 config TOYBOX_SUID
 	bool "SUID support"
 	default y