support middleware in wx.text

example:

    requireAuthenticate = (req, res, next) ->
      mJwc.byOpenId req.user.openid, (userObj) ->
        unless userObj
          return res.text "你还没绑定教务系统账号呢，<a href=\"http://#{config.web.domain}/jwc/bind?openid=#{req.user.openid}\">>>>去绑定</a>"
        req.jwc = userObj
        return next()

    wx.text '学籍', requireAuthenticate, (req, res) ->
      res.text req.jwc