bidForCancel

[kolinko]

Implement a new kind of a bid: "bidForCancel".

• If the winning bidder is a person who did "bidForCancel", the state of the tokens returns to "trading" (that is, the item doesn't change the owner, and everyone keeps their tokens),
• the winning bidder gets the second highest bidder's tokens
• the second highest bidder receives the amount that was sent in bidForCancel
• you can only call "bidForCancel" when the highest bidder isn't "bidForCancel" already
• "bidForCancel" needs to be grater on equal than [price_per_token of highest bidder] * [num_of_tokens of highest bidder]
• regular bids can go after the "bidForCancel" as usual
• (nice to have) if the auction was started by trivial/artist, disable the bidForCancel mechanic

Example:

• the item has 1000 tokens, alice has 100 tokens, and starts the auction, bidding 3 ETH
• bob has 200 tokens, bids 8 ETH - he's the highest bidder now
• charlie calls bidForCancel, paying 2 ETH - he is the highest bidder now

if there are no other bids, and auction time ends:

• Charlie gets Bob's 200 tokens, Bob gets 2 ETH, the contract reverts to the previous state, and people can still trade them, the item doesn't change the owner

but Bob can bid back:

• Bob bids 10 ETH
• auction ends, Bob gets the item

or Alice can bid back

• Alice bids 10 ETH
• auction ends, Alice gets the item