Target zones are now only undefined - we're only evaluating that
behaviour. Also introduced a separate unavailability loss for when the
system overzealously blocks something.
Changed obligation fulfilment behaviour. Now, there's a probability that
in each time step an agent might fulfil one of his outstanding
obligations, and there's a probability that an obligation will 'time
out' and the agent will not be able to recover that utlity.
Fixed a couple of issues with budget and obligation tracking.
Moved risk budget tracking into the requester class - now there are risk
budgets for every requester/owner pair. Makes it comparable with the
trust approach (where each owner uses his own trust model), as with a
global risk budget you have information leakage.