Replace FcObjectStaticName by FcStrStaticName. Implement serialization of

Replace FcObjectStaticName by FcStrStaticName. Implement serialization of
    'object' table (strings pointed to by FcPatternElt->object and used as
    keys) and loading of object table from cache file if more strings are
    present in cache file than in current version of fontconfig. Hash the
    object table in memory.