Make Functions.from typesafe
Remove subscribe(Map<String, Object>)

We considered it being <String, Action> but that is also awkward as it's not a real functional interface.
Also because of type erasure extension methods aren't super helpful here as Map<String, Action> collides with Map<String, Closure>
Merge pull request #3 from benjchristensen/static-core

Remove subscribe(Map<String, Object>) and cleanup Functions.from