SwiftDoc should inherit delegate and superclass docs.

[jshier]

It would be great if SwiftDoc's generated docs could inherit the inline documentation for protocol implementations and overrides. For example, Alamofire has a SessionDelegate type which implements the various URLSession*Delegate protocol methods we're interested in. In Xcode, those methods inherit the documentation from the protocol itself. For example:

SwiftDoc currently generates only the method declarations.

[joshuawright11]

@mattt Any updates on this or tips on getting started to contributing to this feature? Would love it, particularly in the coverage command; I noticed that swift-doc coverage ... flags protocol implementations as undocumented, even if there is documentation at the protocol definition top level.

Happy to hack around on it myself if you don't think it would be super complicated.