请支持自动响应options请求

[wencan]

主流go语言http路由解析组件默认是这么玩的：
当收到options请求，只要请求路径能匹配到路由表中的任一url模式（不管http方法为何），则返回200，否则返回404

目前ssgo不支持该特性，请支持

[xujintao]

Every net/http based http framework can support options method with any url request.
$GOROOT/src/net/http/server.go, line 2733~line 2742

func (sh serverHandler) ServeHTTP(rw ResponseWriter, req *Request) {
	handler := sh.srv.Handler
	if handler == nil {
		handler = DefaultServeMux
	}
	if req.RequestURI == "*" && req.Method == "OPTIONS" {
		handler = globalOptionsHandler{}
	}
	handler.ServeHTTP(rw, req)
}