Add option not to override s and S

[madand]

At first, I would like to thank you for the useful package. Good work! 👍

This PR adds a new boolean option evil-cleverparens-use-s-and-S to prevent shadowing of s and S.

Current code can only detect evil-snipe's use of s and S, with implications on the packages load order. Since I use Avy on s and S, after activation of the evil-cleverparens I ended up without my bindings on these keys. My current workaround is:

(with-eval-after-load 'evil-cleverparens
  (evil-define-key 'normal evil-cleverparens-mode-map
    ;; I use s and S for Avy.
    "s" nil
    "S" nil))

But I feel that having a separate flag for this is a cleaner way to address the issue.

[luxbock]

Sure seems sensible.