Rename JS package to @jupyter/ydoc

[jtpio]

Follow-up to #86

This was discussed elsewhere on the JupyterLab repo.

Now that some of us managed to get a hold on the @jupyter scope on npm, it could interesting to rename this package to @jupyter/ydoc for consistency and early enough before it gets used more downstream.

cc @fcollonval

[fcollonval]

@meeseeksdev please backport to 0.2.x

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout 0.2.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 4b0111f731abca3bc5ad4bd0cff57fcf2cdde2ed

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #97: Rename JS package to `@jupyter/ydoc`'

4. Push to a named branch:

git push YOURFORK 0.2.x:auto-backport-of-pr-97-on-0.2.x

5. Create a PR against branch 0.2.x, I would have named this PR:

"Backport PR #97 on branch 0.2.x (Rename JS package to @jupyter/ydoc)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.

[jtpio]

Opened jupyterlab/jupyterlab#13506 as a follow-up.