unix pipeline stage with before and after preview

(probably only useful if there is a 1-1 relationship between stdin and subproc's stdout)
(it's not at problem if subproc buffers its stdout since it's drained in parallel with stdin)

to install

$ go install go.senan.xyz/beside@master

$ cat names
alice
bob
mick

$ cat names | beside sed "s/.*/\U&/"
alice   ALICE
bob     BOB
mick    MICK

it works for streams too

$ yes yes! | beside yes no! | head -n 3
yes!    no!
yes!    no!
yes!    no!

$ printf "%s\n" "today" "yesterday" "tuesday" | beside date +%s -f -
today      1700851529
yesterday  1700765129
tuesday    1701129600

$ jq <counties_ire.json '.[] | .name' | beside unidecode | column -s $'\t' -t
An Cabhán          An Cabhan
Baile Átha Cliath  Baile Atha Cliath
An Longfort        An Longfort
Ros Comáin         Ros Comain