Revamped concurrency API

[bearophile]

Sean Kelly:

> For what it's worth, I've been experimenting with message-passing for
> one leg of the API.  I decided to copy the Erlang API because it's very
> simple and easy to build fancier stuff on top of.

You may also want to take a look at how actors are in Scala (I think they are a little different than usual, so I think they even have a different name, something like Agents, or something like that):
http://www.scala-lang.org/node/242

Bye,
bearophile