Allow `read` to recognize custom completions

[konsolebox]

`read -e` doesn't recognize custom completions (at least on my basic
observations).  For example, if I enable `complete -IW 'someword
another-word'`, pressing tab on an empty input would do nothing.

I use `read -e` to query for subcommands.  It would be nice if I could
make it autocomplete the commands that are accepted.

Perhaps adding a shell option that enables this or another option to
read like -E would be sensible.

-- 
konsolebox