Generate a level

Generate levels for my game: <describe the space — rooms? platforms?
a grid?>

Requirements:
- Seeded random, so I can reproduce a specific level from its seed.
  Essential for debugging a broken one.
- Guarantee it's completable. Say how you verify that, and what happens
  when generation produces an impossible layout — regenerate, or repair?
- Constraints, not pure randomness: <minimum gap, maximum jump
  distance, no dead ends, at least one of each pickup>.
- Difficulty as an input parameter, and explain what it changes.

Show me how to dump a generated level as text so I can look at fifty
of them quickly and judge whether they're any good.