simplifier: print error message when using old opencc config files.
refactor user_db.

commit dbfc546f9e448eb3c611e38416504d0fb1abdc98
Author: lotem <chen.sst@gmail.com>
Date:   Wed Dec 3 17:56:13 2014 +0800

    compile!

commit 3272bf78a8ab88168763212f9646a3764434c541
Author: lotem <chen.sst@gmail.com>
Date:   Wed Dec 3 16:48:49 2014 +0800

    almost.

commit e50590ba679c4a08a99de3a2d94d50abf9542c43
Author: lotem <chen.sst@gmail.com>
Date:   Fri Nov 21 19:34:33 2014 +0800

    temp.

commit f441c2eb4d6d67a1cf77bd896965e469c94f9faf
Author: lotem <chen.sst@gmail.com>
Date:   Mon Sep 15 20:12:37 2014 +0800

    temp.