item.id is ignored in rss output

[ArtskydJ]

Describe the bug
src/rss2.ts looks at entry.guid, not entry.id as documented (implied) in the readme.
https://github.com/jpmonette/feed/blob/master/src/rss2.ts#L117-L121

Expected behavior

• entry.guid should be documented OR
• the code should look at entry.id instead

Actual behavior
entry.guid is not documented, but is being used.

Versions (please complete the following information):

• feed: I think since version 1.

Additional context
Workaround: submit both the entry.guid and the entry.id

Also, the test didn't catch this issue. If this test line was changed then the tests would catch the issue.
https://github.com/jpmonette/feed/blob/master/src/__tests__/setup.ts#L34

  sampleFeed.addItem({
    title: "Hello World",
-   id: "https://example.com/hello-world",
+   id: "0123456789abcdef-0123-4567-89abcdef"
    link: "https://example.com/hello-world",
    description: "This is an article about Hello World.",

[jpmonette]

@ArtskydJ A PR is welcomed to support this 💪🏼.

[ArtskydJ]

Would you rather have me change the docs to guid, or the code to id?

[KnicKnic]

So I just wasted a bunch of time on this! My personal preference is to remove guid, and bring the rss2 into alignment with atom & json. However this will break backwards compat.

I think the below code would be the best compromise.

    if (entry.guid) {
      item.guid = { _text: entry.guid };
    } else if (entry.id) {
      item.guid = { _text: entry.id };
    } else if (entry.link) {
      item.guid = { _text: entry.link };
    }

[melroy89]

yea pretty strange bug... Please solve :\