Show previous versions of a document's editing history

[awmartin]

Motivation

When writing a documents sometimes I want to see previous content I had written, because I had written content there that I want to reference now or I want to see the change of a doc.

Design

Show a list of revisions on the right-hand side, maybe hidden by a button. Each revision should just be the date and time the revision was saved.

When editing, save a revision every 5 or 10 minutes and when the user navigates away from the doc.