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

grep.sym

@@ -1,53 +0,0 @@
-00000000 grep.c
-00000000 ulib.c
-00000000 printf.c
-00000680 printint
-00000af0 digits.0
-00000000 umalloc.c
-000012a0 freep
-000012a4 base
-00000370 strcpy
-00000730 printf
-0000066b greeting
-00000590 memmove
-000000c0 matchhere
-0000063b mknod
-00000490 gets
-0000060b getpid
-000001d0 grep
-00000960 malloc
-0000061b sleep
-000005d3 pipe
-00000663 getch
-00000633 write
-000005f3 fstat
-000005e3 kill
-000005fb chdir
-000005eb exec
-000005cb wait
-000005db read
-00000643 unlink
-000005bb fork
-00000613 sbrk
-00000623 uptime
-00000e90 __bss_start
-00000430 memset
-00000000 main
-00000310 matchstar
-000003a0 strcmp
-00000673 shutdown
-00000603 dup
-00000ea0 buf
-00000500 stat
-00000e90 _edata
-000012ac _end
-00000170 match
-0000064b link
-000005c3 exit
-00000550 atoi
-00000400 strlen
-0000062b open
-00000450 strchr
-00000653 mkdir
-0000065b close
-000008d0 free