Copyright and id shouldn't be required in Feed typings

[robinmetral]

Describe the bug

copyright and id are required in the typings for FeedOptions (equivalent to "channel" in the RSS 2.0 spec):

https://github.com/jpmonette/feed/blob/fd77835d23990670975092c15009c75432e258ac/src/typings/index.ts#L48-L67

Expected behavior

They shouldn't be required. The only required channel elements are title, link and description (source).

Actual behavior

They're required and the TS compiler complains if they're left out.

Versions (please complete the following information):

(n/a)

Additional context

Is this because we need them for anything else than building the actual RSS channel? Happy to make a PR fixing this if it's unintended.

[paul-uz]

@jpmonette I've just installed this package and spotted this straight away. Can this please be addressed?

id isn't even a valid optional top level element.