Avoid calling Option.get
Don't connect and disconnect a model to the document.

This is entirely unnecessary, an annotation model is connected for the lifetime
of an editor. This gives rise to a race condition in `Save`.

Fixed #24.
Cleanup in error annotations.

Don't accumulate annotations in "previousAnnotations" and don't create error
markers during reconciliation.

Fixed #47.
Merge pull request #52 from dragos/issue/fix-save-failed-24

Save Failed assertion failed and small cleanups in error annotations.