Evaluate a new way to compare handlers.

[nathanhammond]

(From Slack conversation about #242.)

The comparison function to identify equivalency relies on everything coming in at the same time. We should consider a different approach that allows for piece-wise comparison and setting of things like context.

@rwjblue "proposed" setContext as a method, and matchesContext to be part of the evaluation function for equivalency.

Something like this would make it a bit easier to split the responsibilities of checking handler identity into manageable bites.