new completion code in parallel 20220622

[Leah Neukirchen]

Hi,

I'm packaging parallel for Void Linux and have a few notes on the last
release:

1) install-data-hook doesn't respect $DESTDIR when installing completions.
2) install-data-hook assumes parallel is in $PATH when installing completions,
   which is not true when using $DESTDIR; using ./src/parallel instead
   should be fine.
3) Why does the zsh completion eval at runtime instead of generating
   the output at compile time, just like bash?

Thanks,
-- 
Leah Neukirchen  <leah@vuxu.org>  https://leahneukirchen.org/