Add setting to reduce impact of expired moments about sugarcube-2

[david-donachie]

Presumably this would affect how hasVisited() (still works with a map, not with a drop), visited() (can only ever return 1, unless the map stores a counter?) and visitedTags() (presumably reliable with a map, and not a drop), work.

What would you think about something like a State.history.trim(maxVisits) method, which just cuts the history to have no more than X instances of a given passage? That might not really be a gain over using a map to record the number of visits per passage

[tmedwards]

To clarify, and assuming that the previous passage is recorded separately. Simply dropping expired moments will break the (entire) visited family of functions and the <<return>> macro. Switching to a Map([[name, visits]]) would only break the lastVisited() function as it's the only one that depends upon order.

The <<back>> macro and Jump To dialog are affected simply by expiring moments. Changing how expired moments are treated doesn't further affect them.