Sx networks

Provide functionality for retrieving network information as well as keeping track of favorite questions.
Reproducible (`users/337/*` is my account, so using it rather than `me/*` to provide you the same results.)

```lisp
(cl-prettyprint
 (cl-loop for test-site in '(emacs meta.emacs) collect
          (cons test-site
                (sx-method-call
                 "users/337/favorites"
                 `((site . ,test-site))
                 sx-favorite-list-filter
                 'nil))))
((emacs . [((question_id . 3356)) ((question_id . 2497))])
 (meta\.emacs . [((question_id . 3356)) ((question_id . 2497))]))


(cl-prettyprint
 (cl-loop for test-site in '(emacs meta.emacs) collect
          (cons test-site
                (sx-method-call
                 (format "users/337/favorites?site=%s" test-site)
                 nil
                 sx-favorite-list-filter
                 'warn))))
((emacs . [((question_id . 3356)) ((question_id . 2497))])
 (meta\.emacs . [((question_id . 218))]))
```