Replace player with currentPlayer option in setActivePlayers

[delucis]

Supersedes #514, related to #487.

In order to clarify who is being impacted by setActivePlayers calls — especially in hooks — this changes the syntax to require a currentPlayer option instead of a player option:

Breaking Changes

Anyone currently using the setActivePlayers event or the turn.activePlayers option in their game config, who is using a player option may see breaking changes.

Migrating will take one of two forms:

1. Switching to using currentPlayer

   For turn.activePlayers or setActivePlayers calls where player was always the current player in any case, users will only have to rename the option:

   activePlayers: {
   - player: 'A',
   + currentPlayer: 'A'
   }

2. Maintaining player behaviour

   For setActivePlayers calls where the behaviour impacted the player who triggered the move/event specifically, users will need to switch to using the value option, for example:

   ctx.events.setActivePlayers:({
   - player: 'A',
   + value: { [ctx.playerID]: 'A' }
   })

Further considerations

setStage and endStage still rely on playerID, which is unavoidable. These should probably be disabled in onBegin and onEnd hooks for clarity’s sake.