Shell Update & grep fix

This is a minor release as I plan to release a new cx16os video on Youtube

Changes:

shell:

• Pressing the up arrow in the shell now replaces the current buffer with the previous command. This is not comparable to a history as you can only go back once, but I think it will be helpful if you make a typo in a command and want to fix it without retyping the whole line

grep:
-no longer prints garbage on matches

• you can now issue the -n flag (after the pattern) to print line numbers alongside the matches