* riece-alias.el (riece-alias-alternate-separator): New user

* riece-alias.el (riece-alias-alternate-separator): New user
option.
(riece-alias-use-atmark): Abolished.
(riece-alias-escape-alternate-separator): Renamed from
riece-alias-escape-atmark; use riece-alias-alternate-separator
instead of hard-coded "@".
(riece-alias-abbrev-alternate-separator): Renamed from
riece-alias-abbrev-atmark; use riece-alias-alternate-separator
instead of hard-coded "@".
(riece-alias-expand-alternate-separator): Renamed from
riece-alias-expand-atmark; use riece-alias-alternate-separator
instead of hard-coded "@".