doc: update symbols-outline to point to new repo and new config

[luong-komorebi]

Redirect all examples to use the new outline nvim repo
Add a warning to the old symbols-outline documentation and reference back to the commit that addresses compatability issue

[SamuSoft]

I saw this PR after I'd created my issue, but it's now linked here I guess: #100
One thing which has happened since this PR was created is that the new repository has been un-forked, meaning that it now is its own stand alone library. This is reflected in a new file under Extras -> Editor -> Outline, so in this PR it should be fine to drop the changes to the file in docs/extras/editor/symbols-outline.md