Implement tac (closes #117)
Remove a couple of programs from the to-do list
Merge pull request #118 from Arcterus/tac

Implement tac (closes #117)
tac: fix an issue with --separator
Merge pull request #119 from Arcterus/tac

tac: fix an issue with --separator
Add paste (closes #120)
paste: make MUCH faster and fix a couple bugs
Remove paste from the to-do list
Merge pull request #122 from Arcterus/paste

Implemented paste
mkdir: improve error handling (closes #121)
Merge pull request #123 from Arcterus/mkdir

mkdir: improve error handling (closes #121)
stty in progress
Merge pull request #124 from alan-andrade/patch-5

stty in progress
allow uppercase variables for du
Merge pull request #125 from Heather/master

allow uppercase variables for du
expand in progress
Merge pull request #128 from Doppp/expand_in_progress

expand in progress
Add basic structure of `cp`
Implement basic file copying

Assumes there is only one source and one destination. Corresponds to the `cp
SOURCE DEST` usage documented in `man cp`. No options are implemented.
Remove file existence check; add equivalency check

GNU `cp` does not require that the destination not exist in the case of `cp
SOURCE DEST` usage as I previously thought; that check has been removed.
However, it does error if the paths given refer to the same file, (traversing
symlinks); a check for that was added.