连接多个字符串.
(dos_strcat [string [string] ... ])
string
字符串.
如果成功, 返回连接后的字符串. 如果未提供参数则返回零宽度字符串("").
nil 失败时.
Command: (dos_strcat "Hockey " "is " "the " "best.")
"Hockey is the best."