Allow the user to provide "describers" on a per-handler basis.

[jmalloc]

It might be useful if the user could provide a function that can describe the current state of a projection (or perhaps any other handler) so that it can be observed when a test fails and/or between each engine dispatch/tick.

I am not sure how much merit this idea has; specifically, I wouldn't want devs to spend forever writing and updating code that exports SQL database state in a human readable format. For SQL projectionkit could help with that, but obviously projections are not limited to any particular storage technology.

This is also potentially a LOT of data, possibly too much to include in an expectation report, but I suppose it could be written to disk and the expectation report could print the file location. Another option would be to reimplement some kind of verbose option.

[jmalloc]

We might need to look at #5 for this feature to be very useful.

[jmalloc]

This could be done in a VERY generic way by simply having a function that returns some content that is diffed each time a fact occurs. It wouldn't even need to be aware of handlers.