gensubst: Unify quoting into 'quote' substitution
gensubst: Unify quoting into 'quote' substitution

Instead of applying each level of quoting separately, construct a large
sed(1) script from particles and apply that to the QUOTEE once, thus
also increasing performance. Moreover, *all* types of quoting are able
to deal with multi-line QUOTEEs now.

For backward compatibility, retrofit 're'/'rs'/'sh' substitutions to the
unified 'quote' substitution by shuffling parameters in phase 1.

donkarlos/libdl-sh