Document OPT_SAVEGAMESCREENSHOTLAYER in Globalfunctions_General

[ericoporto]

https://github.com/adventuregamestudio/ags-manual/wiki/Globalfunctions_General#setgameoption

Added new game-wide option OPT_SAVEGAMESCREENSHOTLAYER that lets to define which of the game's render layers will be captured when making a standard screenshot for the save game.

RenderLayer is documented in #259 , and screenshot is discussed in #258

Example

function game_start()
{
  SetGameOption(OPT_SAVEGAMESCREENSHOTLAYER, eRenderLayerRoom);
}

This option was added in PR adventuregamestudio/ags#2526