Use cl-lib in slime-fuzzy.el

* contrib/slime-fuzzy.el (slime-fuzzy-completions)
(slime-fuzzy-complete-symbol)
(slime-fuzzy-insert-completion-choice)
(slime-fuzzy-fill-completions-buffer)
(slime-fuzzy-insert-from-point, slime-fuzzy-select): Use cl-lib.
Improve support for strings in (:export ...) clause

* contrib/slime-package-fu.el (slime-export-symbols): Handle strings.
(slime-defpackage-exports): Use `slime-export-symbols' and strip
double quotes.
(slime-frob-defpackage-form): Don't skip package name in case
(:export ...) is immediately following.
(slime-determine-symbol-style): Support double quoted styles.