Allow editing of previously recorded results

[istathar]

We have had the problem that if the user inadvertently presses <Enter> one too many times they will record a result that was unintended and incorrect. Further, as a learning matter, if someone has entered a value and then realizes it needs amending, there was no way to edit it.

This branch introduces the Revoke state to the PFFTT format which invalidates a previously recorded result, allowing the trail to be re-run from that point and values downstream of it re-prompted for. This also updates the PFFTT file format to include a serial for each scope. Together with the path address it now uniquely identifies an iteration of an invocation (whereas the path alone does not).

Pressing <Up> at a live prompt now enteres a "navigation" mode where the user can step back through what the run has already recorded. At a position that already had a result recorded, <Esc> opens menu and offers Edit to change the value

The behaviour of this "navigation" is somewhat complex, so a .moves file is added to the test suite to show what the expected location is after different keystroke permutations from each position.

Internally, keystroke procesing and dispatch have been refactored into two separate layers. The first maps a KeyEvents to an Intents. The second handles those Intent depending on the context.

[istathar]

Updates implementation of:

• Define PFFTT for use in running Technique documents specification#9