Review every command defined in `repl` and clean up their error messages. For inspiration, review the original Fortran subroutines. Add the name(s) of the relevant subroutines and the files they came from to the function description would also be a good idea. A list of commands to tick off. ``` Top level: ADD BACK BULLETIN CHANGE COPY CREATE Ctrl-C CURRENT DELETE DIRECTORY EXIT FIRST Folders FORWARD HELP INDEX Keypad LAST MAIL MARK MODIFY MOVE NEXT PRINT QUIT READ REMOVE REPLY RESPOND SEARCH SEEN SELECT SET SHOW SSH UNMARK UNSEEN USER SET: ACCESS ALWAYS BRIEF DEFAULT_EXPIRE EXPIRE_LIMIT FOLDER NOACCESS NOALWAYS NOBRIEF NOPROMPT_EXPIRE NOREADNEW NOSHOWNEW NOSYSTEM PROMPT_EXPIRE READNEW SHOWNEW SYSTEM SHOW: FLAGS FOLDER -NEW PRIVILEGES USER VERSION SSH: ADD DELETE FETCH LIST USER: ADD ADMIN DELETE DISABLE ENABLE LIST MOD NAME NOADMIN NOMOD ```