New conduit-interpreter approach, using actions as input.

Yet another interpreter, which is better than the previous one, but
still useless. Next, I'll show the benefits/drawbacks of this
approach:

+ It works
+ It's nice the way the result is generated (by the sink).
+ It's a proof that IORefs is as good as State for this concern.
+ We can keep the inner state at the sink.

- We haven't use any conduit. In fact, we use Source and Sinks in a
  forced manner, since they're unnecessary.
- The important task (keeping the next state) is achieved by the
  surrounding IORef.
- In theory, we could think that Actions are a good example of a
  chunk. In practice, with Free Monads application, this is impossible
  since we need the result of the previous actions to fulfill the rest
  of them (think of: ref <- Put "hola"; Get ref).
- The state is kept as a whole. This requires further researching, but
  I'm afraid it won't be easy to be splitted.
- Passing IORefs around is kind of ugly.