Retire awaynick (resolves #661)

debug output on startup:

    [ .. ] Loading network module [awaynick]...
    [ >> ] NOTICE: retired module - see http://wiki.znc.in/awaynick [./modules/awaynick.so]

loadmod client command:

    <jpnurmi> loadmod awaynick
    <*status> Loaded module [awaynick] NOTICE: retired module - see
              http://wiki.znc.in/awaynick [./modules/awaynick.so]

any module command:

    <jpnurmi> help
    <*awaynick> The module was retired - see http://wiki.znc.in/awaynick

loading the module via webadmin notifies:

    NOTICE: retired module - see http://wiki.znc.in/awaynick [./modules/awaynick.so]