evil-args-delimiters an alist of mode→delimiter?

how about making `evil-args-delimiters` an assoc-list, so you can have more modes do the right thing out-of-the-box, e.g.

```
'((emacs-lisp-mode '(" "))
  (weird-mode #'weird-mode-arg-matcher-function
  (t '("," ";")))
```
