Implement a bounty system modeled on SO bounties.

Bounty system

  • Assign bounty to question
  • bounty comes from question owner's point pool
  • bounty expires after a period of time (1 week?)
  • bounty awarded by question owner
  • 1 more day to award bounty?
  • automatic bounty award to upvoted answers?
  • repeatedly offer bounty?
  • cannot cancel bounty