Add Notebook support

[KamasamaK]

Fixes #640

[pisv]

I have checked it against the spec. Great work, as always! Minor suggestions attached.

[pisv]

LGTM. Thanks!

[Cyrik]

So I tried using the PR and I noticed that org.eclipse.lsp4j.services.LanguageServer has no getNotebookDocumentService method. Is there some other way to plugin my own NotebookDocumentService implementation?

[KamasamaK]

@Cyrik Sorry. This is my first time adding a new service, so I missed some things.

[Cyrik]

No problem at all, thank you for the fast update! I didn't notice the missing bit either until I wanted to pass in my service 😄
I'll try it out tomorrow.

[Cyrik]

I just tried to use the new version but there seems to be no snapshot of it. Can I somehow trigger the build myself?

[pisv]

It looks like this build includes the latest changes, does not it?

[Cyrik]

ah yes, thank you. I didn't find that link and was trying to use the nightly or build it myself 😅
The one you posted worked and after a bit of jvm version switching, I can also build my own. I've got capabilities to work from Clojure, going to try the actual sync messages tomorrow. Thank you.

[Cyrik]

I've tested all the notebookDocument/* calls and they work for me! Capabilities also produce the correct results. So I'd be happy to have this merged and base our next LSP version on it.
Thank you for integrating this quickly!