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

hello.sym

@@ -1,48 +0,0 @@
-00000000 hello.c
-00000000 ulib.c
-00000000 printf.c
-00000320 printint
-00000758 digits.0
-00000000 umalloc.c
-000009f8 freep
-000009fc base
-00000010 strcpy
-000003d0 printf
-0000030b greeting
-00000230 memmove
-000002db mknod
-00000130 gets
-000002ab getpid
-00000600 malloc
-000002bb sleep
-00000273 pipe
-00000303 getch
-000002d3 write
-00000293 fstat
-00000283 kill
-0000029b chdir
-0000028b exec
-0000026b wait
-0000027b read
-000002e3 unlink
-0000025b fork
-000002b3 sbrk
-000002c3 uptime
-000009f8 __bss_start
-000000d0 memset
-00000000 main
-00000040 strcmp
-00000313 shutdown
-000002a3 dup
-000001a0 stat
-000009f8 _edata
-00000a04 _end
-000002eb link
-00000263 exit
-000001f0 atoi
-000000a0 strlen
-000002cb open
-000000f0 strchr
-000002f3 mkdir
-000002fb close
-00000570 free