Add support for high bit depth multichannel images

[aclark4life]

Fixes #1888 .

Changes proposed in this pull request:

• Add support for high bit depth multichannel images

[aclark4life]

And… can't push to this PR … is that expected? I renamed newconfig to mb_config and then I get:

(pillow) λ ~/Developer/pillow/pillow/ hack202406 git push origin HEAD:refs/pull/8223/head --force-with-lease
Enumerating objects: 175, done.
Counting objects: 100% (175/175), done.
Delta compression using up to 8 threads
Compressing objects: 100% (58/58), done.
Writing objects: 100% (135/135), 25.46 KiB | 12.73 MiB/s, done.
Total 135 (delta 115), reused 96 (delta 77), pack-reused 0
remote: Resolving deltas: 100% (115/115), completed with 38 local objects.
To github.com:python-pillow/Pillow.git
 ! [remote rejected]     HEAD -> refs/pull/8223/head (deny updating a hidden ref)
error: failed to push some refs to 'github.com:python-pillow/Pillow.git'
(pillow) λ ~/Developer/pillow/pillow/ hack202406 

[yoursunny]

And… can't push to this PR … is that expected?

This is expected, because you created this PR from my repository.
If you can push to the PR, it means you are able to write to my repository, without my authorization.

I have created #8224, in which I gave permission for maintainers to write to the yoursunny:multiband branch.
You can try updating there.

yoursunny:hack202406 will stay where it is, because it is intended to represent my @MoCoMakers hackathon submission.