Print the type's help for undocumented bindings

[mbauman]

In 0.3:

julia> sparse([1,2,3]);

help?> ans

    [1, 1]  =  1
    [2, 1]  =  2
    [3, 1]  =  3 is of type
DataType   : SparseMatrixCSC{Int64,Int64} (constructor with 1 method)
  supertype: AbstractSparseArray{Int64,Int64,2}
  fields   : (:m,:n,:colptr,:rowval,:nzval)

Currently:

help?> ans
search: ans transpose transpose! ctranspose ctranspose! randsubseq randstring

This was a nice way to explore an API. It'd be nice for an undocumented binding/object to print out its type and the type's help (which is much nicer now with #12996).

[MichaelHatherly]

Yeah, would be good to have. I didn't really like the way it echoed the object itself since sometimes that would be distracting if it's a large object.

This would probably just need some minor changes to

julia/base/docs/Docs.jl

Lines 98 to 101 in 5edd47c

	function doc(b::Binding)
	d = invoke(doc, Tuple{Any}, b)
	d == nothing ? doc(getfield(b.mod, b.var)) : d
	end

I think.