There was a time, not too long ago, when cruise passengers wishing to occupy a cabin by themselves had to pay a supplement of up to 200% of the double-occupancy fare. Increasingly, though, cruise lines are catering to solo travelers with cabins that require no penalty for single occupancy. Solo cabins were something of a rarity on modern cruise ships, which favored staterooms designed for two or more until Norwegian Cruise Line started the trend in 2010 aboard the Norwegian Epic. Now, many other cruise lines are jumping on the single-cabin bandwagon. What follows is a quick rundown of choices …