Bug#639221: replace folding.el with elpa-folding

[David Bremner <david@tethera.net>]

Nicholas D Steeves <nsteeves@gmail.com> writes:

>
> I'm not convinced this one is more suitable for the Debian archive
> than the alternatives, but if you consent to being an Uploader for
> Jaalto's folding-mode (continuation of the goodies one) then I'm
> willing to package it:
>   https://github.com/jaalto/project-emacs--folding-mode/
>

Our (or at least my) goal in this instance is not to package the best
possible things, but to provide the smoothest transition for users of
emacs-goodies-el. That means having the keybindings they are used to
work in the same way (to the degree that is possible even with the same
package).