POST handler of auction_brandt extension now parses JSON transcript and
passes JSON via stdin to external program. Reads result via stdout.
TODOs:
- check signatures in transcript
- parse JSON output of replay progam
- add configuration to to auction_brandt:
- types of auctions
- max. concurrent users
- max. number of prices
- maximum price
- fees
- add timeout handler for replay program execution
- (maybe) sign output of exchange by master-key
- (maybe) add GET handler with information re: auction_brandt?
