Round management
----------------
-• Add a /round command to create a new round. This is like a puzzle in
- that it has its own channel, but different in that it doesn't accept
- a solution, etc.
+• Group the puzzles in the Turbot home view by round
-• Add an (optional) drop-down at puzzle creation for selecting a known
- round for a puzzle, (or creating a new round). Ensure this mechanism
- allows for puzzles to exist in multiple rounds.
+• Select round fields by default based on the round of the puzzle for
+ the channel in which `/puzzle` is invoked.
• Consider putting a round prefix into the channel name to group a
round's puzzles in the channel list.