Document ListBox updated APIs

[ericoporto]

https://github.com/adventuregamestudio/ags-manual/wiki/ListBox

• In ListBox.FillDirList, the fileSortStyle and sortDirection parameters were added
• In ListBox.FillSaveGameList, the min_slot and max_slot parameters were adeed

From changelog in the forums

• Added FileSortStyle and SortDirection enum, and optional "fileSortStyle" and "sortDirection" parameters to ListBox.FillDirList(). This lets to sort resulting list by name or time, in ascending or descending order.
• ListBox.FillSaveGameList(), RestoreGameDialog() and SaveGameDialog() now let define a range of save slots for display.

	/// Fills the list box with all the filenames that match the specified file mask.
	import void FillDirList(const string fileMask, FileSortStyle fileSortStyle = eFileSort_Name, SortDirection sortDirection = eSortAscending);
	/// Fills the list box with the current user's saved games in the given range of slots.
	import int  FillSaveGameList(int min_slot = 1, int max_slot = 100);

Added in PR adventuregamestudio/ags#2541