get_object_list callback prefix field should be Vec<String>

[weekitmo]

this is the result when i use nodejs to test.

When using prefix and delimiter to query together, prefixes means the sub folder that contains prefix。in my case, i print &response.prefix() only the last one string.

reference：

https://help.aliyun.com/document_detail/84841.html#p-awp-qxy-gu1

[weekitmo]

    fn set_prefix(&mut self, prefix: &str) -> Result<(), Self::Error> {
        if self.prefix == ""  {
            self.prefix.push_str(&prefix.to_owned())
        } else {
            self.prefix.push_str(format!(",{}", &prefix.to_owned()).as_str());
        }
        
        Ok(())
    }

and use it

    let prefixes = response.prefix();
    let vec_prefixes: Vec<&str> = prefixes.split(",").collect();
    for pre in vec_prefixes {
        // TODO
    }

This is my adjustment. Maybe you have your own ideas

[tu6ge]

I look at aliyun docs, and find CommonPrefixes and Prefix is two different field of response.

so, ObjectList should add a new filed. used by save CommonPrefixes info

[weekitmo]

pretty good