Declarative Language Syntax

[erikh]

Now that we've separated the execution context and language evaluator, we can support multiple languages without having to implement all the builder logic again.

What I'd like to introduce is a YAML-alike declarative syntax. This would work similarly to Ansible and of course would assume the same API as the mruby implementation.

Rationale: many have complained about the use of ruby in the builder, discarding the features box supports. This gives those people an alternative.