Include public extensions of external types

[sindresorhus]

It seems like swift-doc does not include extensions. My project has a NSMenuItem extension, which would be nice to also include. Jazzy correctly includes this.

Screenshot:

Live example: https://sindresorhus.com/KeyboardShortcuts/Extensions/NSMenuItem.html

[mattt]

That's a great idea. Thanks for pointing this out, @sindresorhus!

[tanner0101]

+1 this would be very helpful for Vapor's API docs (https://api.vapor.codes). Some of our packages actually consist only of extensions so attempting to generate docs on them fails (https://github.com/vapor/fluent-postgres-driver for example).

[GalenRhodes]

I would like to upvote this feature!!!! Then I can stop using Jazzy which is slower than molasses running uphill in January.

@mattt: I appreciate your enthusiasm for this feature, and am working to implement it in the next release. However, I marked this comment as off-topic because of the remark about Jazzy, which doesn't meaningfully contribute to discussion.