Implement fold

STATUS: move hash to N/A

This is a shell builtin

Implemented pwd

Implement tee

Implement echo

The behaviour of echo command is to print exactly as the arguments are,
unless -n is in which the escape chars are recognized.

Implement nohup

Implement sleep

Implement env

Add dirname

Implement rmdir

Implement head

Implement comm

Implement logname

Implementation of the getlogin(3) function tend to be terrible in
C libraries, but the POSIX standard requires that logname uses it.

Implement link

Implement tty

Implement nice

STATUS: mark unlink as done

STATUS: move talk/write out of scope

These are part of the User Portable Utilities option.

Implement cmp

Implement cksum

Formalize definition of scope