Whiskey fever is sweeping the nation. Every day, craft distilleries are popping up in remote counties and urban centers, offering a wealth of great choices to consumers-and just as many puzzlements. Does the introduction of a simple ''e'' to go from whisky to whiskey mean anything? What's the difference between Scotch and Rye? What's Canadian whisky anyway? And what about the whiskeys of Scotland, Japan, and Ireland? Where's a humble Joe to start?