Add the new `link_to` argument to the example to show how it's used.

This reverts commit 28db706443a912e8355e4c48488dc40c403e7f76.

Turns out we didn't need to be able to pass an arbitrary number of
arguments to the lambda after all. The URL helper objects necessary in
addition to the first argument to the lambda can be retrieved from the
view context directly instead of passing them into the block as
parameters (which would actually make things more difficult, because the
block is called in the `TableBuilderHelper`, thus outside the scope of
the view).

This enables us to pass multiple objects into the lambda, so that we can
for example build a URL using a Rails helper using multiple objects.

Example:

    column.link_to(referential, item)

    lambda do |referential, item|
      some_path(referential, item)
    end

Instead of always linking to the `name` and `comment` attributes, allow
any column to link to any thing by calling the new
`TableBuilderHelper::Column#link_to` method.

Because `linkable?`-ness is now determined at the column level, we can
get rid of the `#column_is_linkable?` method here.

The code is still pretty much "en désordre" as a result of the
`overhead` code tornado, but we'll have to deal with that later. (Oh
goodness I hope we get to deal with it.)

Testing out the new `TableBuilderHelper::Column#link_to` method to
provide the link needed to go to the row object's #show page.

Seems to work in this context, which is promising!