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

cat.sym

@@ -1,50 +0,0 @@
-00000000 cat.c
-00000000 ulib.c
-00000000 printf.c
-00000420 printint
-00000890 digits.0
-00000000 umalloc.c
-00000d80 freep
-00000d84 base
-00000110 strcpy
-000004d0 printf
-0000040b greeting
-00000330 memmove
-000003db mknod
-00000230 gets
-000003ab getpid
-00000090 cat
-00000700 malloc
-000003bb sleep
-00000373 pipe
-00000403 getch
-000003d3 write
-00000393 fstat
-00000383 kill
-0000039b chdir
-0000038b exec
-0000036b wait
-0000037b read
-000003e3 unlink
-0000035b fork
-000003b3 sbrk
-000003c3 uptime
-00000b74 __bss_start
-000001d0 memset
-00000000 main
-00000140 strcmp
-00000413 shutdown
-000003a3 dup
-00000b80 buf
-000002a0 stat
-00000b74 _edata
-00000d8c _end
-000003eb link
-00000363 exit
-000002f0 atoi
-000001a0 strlen
-000003cb open
-000001f0 strchr
-000003f3 mkdir
-000003fb close
-00000670 free