Verbose REPL help mode

[c42f]

As discussed at the juliacon hackathon, it would be cool to have a verbose help mode in the repl, perhaps triggered by typing ?? at the start of a line.

This could dump out the autogenerated documentation for a method or type in addition to the docstring. @StefanKarpinski also suggested an optional Dev docs section in the docstring which could also be dumped out in verbose help mode:

"""
End user docs

# Dev docs
Internal documentation of internal details, etc
"""
function foo()
end

[rfourquet]

Would this be closed by #34226?

[c42f]

It's similar, though it still might be nice to have a way to request the autogenerated documentation showing the structure of a struct

[mkitti]

Maybe the autogenerated documentation could be access via ??? since ?? is now Extended Documentation