Documented the aux-item definition file format.
               Updated the database format documentation.

Server:        Implemented aux-items.
               Checked error returns and set error-status to something
                   useful in most cases.
               New RPC calls:
                   create-text
                   create-anonymous-text
                   create-conf
                   create-person
                   get-text-stat
                   get-conf-stat
                   modify-text-info
                   modify-conf-info
                   get-info
                   modify-server-info
                   get-collate-table
                   set-expire
                   query-unread-texts
               New asynchronous messages:
                   new-text
                   deleted-text