Atomic event sequences

This is a new file for `./examples`.

I am trying to write functions that group sequences of query and update events into one atomic transaction.  I don't think this functionality exists in acid-state, but I feel there must be some idiom to handle this less clumsily than I did.

This is mostly a request for comments:

1. Is there a simple, elegant solution for atomic sequences of events that I have missed in my example?
2. If not, would a pull request with that functionality in local-state have a chance of getting accepted?