todo: a todo list manager
requires standard POSIX utils and mktemp

install:
copy to anywhere in your $PATH

relevant variables:
	$EDITOR (preferred editor, uses vi if blank)
	$TODO (path to todo file, uses $HOME/todo if blank)

options:
[no args]	shows todo file with numbered lines
-e		edits $TODO in $EDITOR
-x		shows completed tasks
-n num		operate on line num
-a string	add string to todo
-d [num]	delete line num


trick:
todo -n 10 -a 'string'
	will place string at line ten, pushing each line after it down by one