need a flag for "log to a file"

need a flag for "log to a file"

./ilts -e foo 

and we log to foo-20161231_150304.log with no stdout

and we can add -j to not prepend time stamps

./ilts --just-log foo
and
foo-20160102.150405.log will be created in append mode

-j|--just-log =>    --printf-format "%s%s\n" --time-format=""
and
-e|--expected-filename =>   -append --time --suffix .log --prefix ${arg}-
