Added buffer to the console

Added hotkeys to switch between console buffers and to return to the home one
Added clear screen command
Added debug text outputs to the hello command and when loading sh

Makefile

@@ -199,6 +199,7 @@ UPROGS=\
 	_shutdown\
 	_argtest\
 	_screen\
+	_cls\
 
 fs.img: mkfs $(UPROGS)
 	./mkfs fs.img $(UPROGS)
@@ -222,7 +223,8 @@ QEMUGDB = $(shell if $(QEMU) -help | grep -q '^-gdb'; \
 	then echo "-gdb tcp::$(GDBPORT)"; \
 	else echo "-s -p $(GDBPORT)"; fi)
 ifndef CPUS
-CPUS := 2
+#CPUS := 2
+CPUS := 1
 endif
 QEMUOPTS = -drive file=fs.img,index=1,media=disk,format=raw -drive file=xv6.img,index=0,media=disk,format=raw -smp $(CPUS) -m 512 $(QEMUEXTRA)