Port to Drupal 8

There is now a 8.x-1.x-dev release, although it's fairly minimally tested at this point.

I've ported this module to D8: https://github.com/grasmash/drupal-alt-stream-wrappers

Notable changes from the current 8.x-1.x-dev branch:

• The stream wrapper was renamed to alttemporary://. This is based on restrictions on the use of special characters in stream wrapper names.
• The stream wrapper base path is now stored in Config, not in Settings. This is consistent with how core stores filepaths for other streams.
• New KernelTests have been added and are passing.
• Druplaci.yml has been added. We'll see how it does once code is pushed to Drupal.org.
• Composer.json was added.
• There is now a settings form available via the UI at /admin/config/media/file-system, where you can set the file path for the stream wrapper.

Note also that, as before on 8.x-1.x-dev, the scope of the Drupal 8 version is just to add a single, additional `alttemporary://` stream wrapper.

Next step:
Please review and push new commits to Drupal.org.

If you'd like to make me a co-maintainer, I can push the code, update the project page, and cut a tag, and publish a release.

8.x-1.0-beta1 was released. Closing. Please open new issues against that the 8.x-1.x branch.

Thanks grasmash!