There is actually NO upgrade path from the Drupal 7 to the Drupal 8 versions for
now and for the forseeable future too.

The main reason for this is that the module was actually completely re-written
from scratch for Drupal 8 and significant changes have been made to pretty much
every part of it.

Notable changes
---------------

* All configuration has been moved to the new YML format.

* All widgets are now expected to define a theme function to handle returning
  their markup. What this means is that the output of all widgets can now be
  easily altered in the same way as any other theme function.

* We now include a Pinterest widget by default.

* We now include an example module that shows how to create a custom widget.