Improve mechanism for communicating with the auction model

[EdNoepel]

The current implementation of auction-keeper uses STDIN and STDOUT to communicate with the auction model. This is a somewhat inelegant mechanism for achieving IPC.

To resolve, consider other mechanisms, such as a websockets connection or an interface consumed by the auction model. Consider structuring auction-keeper to use either mechanism via a configuration parameter. The implementation shall ensure code which implements the auction model can be maintained separate from the auction-keeper.