Buy dai when the system is in surplus.
Can be thought of as buy and burn. Given a net Dai balance, sell the Dai in
return for PETH, which is burned.
$ dai boom <amount-in-skr>
$ seth send "1383193339611678105810169541746055541819509028773" "boom(uint256)" "<amount-in-skr>"
boom(self, amount_in_skr: Wad) -> Transact: