I want to be able to see the history of a reading list.

[e-e-e]

This is possible already with hyperdb, but because of the way hyper-readings stores information as a graph which is then rendered by hyper-reader only some versions will be open correctly. We need to establish a version tagging system so that we know which points in the history of the db represent 'saved' moments.

[e-e-e]

My thoughts for this is to store versions as key/values in hyperdb to flag points in time. For example:

@saved: { version: 1, time: '2018-06-19T11:53:44.264Z'}

We can then traverse the history of the key to checkout older versions of the hyper-reading.
This PR should help us achieve this by adding the ability to stream a keys history to hyperdb -mafintosh/hyperdb#138.