Track which interactions and examinations the player has done

Store all the interactions and examinations the player has done into a list, ordered by time.

Could be used for e.g. a hint system - if the player has seen this and done that but not solved this puzzle, clicking on the player character gives a hint towards the solution.

Makes the feature set of the engine more complex, though.

Requires #17

Might be useful for data gathering about playing of the game. For example, do players see some (optional) content that they're expected to find?

No files, tests, or entry points are named. First review issue #17 and decide how interactions and examinations should be represented and recorded; the work is done when the player's actions are stored in time order for later hint or play-data use.

Written by the indexing model from the issue text.