contrib/lisp/org-contacts.el: Permit to unload properly `org-contacts'

* contrib/lisp/org-contacts.el (org-contacts-setup-completion-at-point):
Setup `completion-at-point-functions' in a dedicated function so it's
easier to add and to remove it from `message-mode-hook'.
(org-contacts-unload-hook): This function removes all hooks added while
loading `org-contacts' in order to respect Emacs coding conventions.
contrib/lisp/org-contacts.el (org-contacts-vcard-format): Silence byte-compiler

* contrib/lisp/org-contacts.el (org-contacts-vcard-format): Silence byte-compiler.
ox-html: Fix code typo

* lisp/ox-html.el (org-html--build-meta-info): Fix code typo.