mu4e: switch to contexts

lisp/init-mu4e.el

                            (mu4e-message-contact-field-matches msg
                                                                :to "aliced@home.example.com")))
            :vars '( ( user-mail-address	    . "aliced@home.example.com"  )
-                    ( user-full-name	    . "Alice Derleth" )
+                    ( user-full-name	    . "ßingen" )
                     ( mu4e-compose-signature . nil)))
          ,(make-mu4e-context
            :name "Work"
                          (when msg
                            (string-match-p "^/Arkham" (mu4e-message-field msg :maildir))))
            :vars '( ( user-mail-address	     . "aderleth@miskatonic.example.com" )
-                    ( user-full-name	     . "Alice Derleth" )
+                    ( user-full-name	    . "ßingen" )
                     ( mu4e-compose-signature . nil)))
 
          ,(make-mu4e-context
                          (when msg
                            (string= (mu4e-message-field msg :maildir) "/cycling")))
            :vars '( ( user-mail-address	     . "aderleth@example.com" )
-                    ( user-full-name	     . "AliceD" )
+                    ( user-full-name	    . "ßingen" )
                     ( mu4e-compose-signature  . nil)))))
 
 ;; set `mu4e-context-policy` and `mu4e-compose-policy` to tweak when mu4e should