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

echo.sym

@@ -1,48 +0,0 @@
-00000000 echo.c
-00000000 ulib.c
-00000000 printf.c
-00000380 printint
-000007c0 digits.0
-00000000 umalloc.c
-00000a74 freep
-00000a78 base
-00000070 strcpy
-00000430 printf
-0000036b greeting
-00000290 memmove
-0000033b mknod
-00000190 gets
-0000030b getpid
-00000660 malloc
-0000031b sleep
-000002d3 pipe
-00000363 getch
-00000333 write
-000002f3 fstat
-000002e3 kill
-000002fb chdir
-000002eb exec
-000002cb wait
-000002db read
-00000343 unlink
-000002bb fork
-00000313 sbrk
-00000323 uptime
-00000a74 __bss_start
-00000130 memset
-00000000 main
-000000a0 strcmp
-00000373 shutdown
-00000303 dup
-00000200 stat
-00000a74 _edata
-00000a80 _end
-0000034b link
-000002c3 exit
-00000250 atoi
-00000100 strlen
-0000032b open
-00000150 strchr
-00000353 mkdir
-0000035b close
-000005d0 free