such that backward-sexp correctly skips them.
(perl-font-lock-keywords-2): Use regexp-opt.
(perl-font-lock-syntactic-keywords)
(perl-font-lock-syntactic-face-function): Better handle PODs.
Handle package names with ' in them and ($$) in `sub' declarations.
Handle format staements. Handle regexp and quote-like ops.
(perl-empty-syntax-table): New var.
(perl-quote-syntax-table): New fun.