Parsing atom feeds without `xml:base` does not resolve relative links

Expected behavior

Absolute link in ParseURL.

Actual behavior

Relative links are provided as is.

Steps to reproduce the behavior

script to test:

package main

import (
    "fmt"
    "github.com/mmcdole/gofeed"
)

func main() {
    parser := gofeed.NewParser()
    feed, _ := parser.ParseURL("https://bou.ke/feed.xml")
    fmt.Println(feed.Link)      // outputs "/"
    fmt.Println(feed.FeedLink)  // outputs "/feed.xml"
}

partial file content:

<feed xmlns="http://www.w3.org/2005/Atom">
    <generator uri="https://jekyllrb.com/" version="4.0.1">Jekyll</generator>
    <link href="/feed.xml" rel="self" type="application/atom+xml"/>
    <link href="/" rel="alternate" type="text/html"/>
    <updated>2020-07-13T09:26:52+00:00</updated>
...

Full feed is provided here: bouke.xml

Notes

Given that such links have to be handled manually in Parse, ParseString methods anyways, I'd like to hear opinions on whether it's worth implementing the fix, or should be the library users' responsibility.

mmcdole / gofeed

Parsing atom feeds without `xml:base` does not resolve relative links #155

Expected behavior

Actual behavior

Steps to reproduce the behavior

Notes